How does one deal with the 'fear of rebirth'?

In Mahayana we make the vow to keep getting reborn so we can keep relearning and then spreading the Dharma until there are no more beings left in samsara.

You may consider that.

Sentient beings are numberless - we vow to save them
Desires are inexhaustible - we vow to end them
The Dharmas are boundless - we vow to master them
The Buddha's Way is inconceivable - we vow to attain it.

But seriously, I don't think you're afraid of rebirth - I think you're afraid of failure. That's what you should be working on. Why is it so frightening for you to be a failure? Whose judgment do you need to satisfy?

Its not death but rebirth that I have developed aversion towards.

How do I address this? How do I get equianimous towards this idea?

By recognizing a few things:

1. Unless one's already enlightened, rebirth will happen anyway, regardless of whether one likes it or not. Recognizing that one's dread or favor over it won't help would hopefully gives one some peace of mind and equanimity.

2. Try to conduct oneself with wholesome deeds thru the 3 gateways: body/speech/mind. If rebirth will happen anyway, it'd be better to have a more peaceful and favorable rebirth due to wholesome kamma than a horrific one due to evil kamma.

You're afraid of being reborn over and over again forever, facing suffering again and again, and of relearning all of this over and over again.

Yet some others are afraid of death, because they don't believe in rebirth and think that they will cease to exist at death. They don't want to stop existing. They are afraid of ceasing to exist.

Both of these appear to be opposite, but they are really two sides of the same coin. They are symptoms of the same disease (dis-ease). The fear arises from clinging to something that is impermanent and unstable.

SN 44.6 explains this in a variety of ways including the following. Although it says Tathagata, it really applies to you too! Do you think you exist after death? Do you think you do not exist after death? Do you think you both exist and do not exist after death? Do you think you neither exist nor do not exist after death?

(i. The aggregates)

"For one who loves form, who is fond of form, who cherishes form, who does not know or see, as it actually is present, the cessation of form, there occurs the thought, 'The Tathagata exists after death' or 'The Tathagata does not exist after death' or 'The Tathagata both exists and does not exist after death' or 'The Tathagata neither exists nor does not exist after death.'

"For one who loves feeling...

"For one who loves perception...

"For one who loves fabrications...

"For one who loves consciousness, who is fond of consciousness, who cherishes consciousness, who does not know or see, as it actually is present, the cessation of consciousness, there occurs the thought, 'The Tathagata exists after death' or 'The Tathagata does not exist after death' or 'The Tathagata both exists and does not exist after death' or 'The Tathagata neither exists nor does not exist after death.'

"But for one who doesn't love form, who isn't fond of form, who doesn't cherish form, who knows & sees, as it actually is present, the cessation of form, the thought, 'The Tathagata exists after death' or 'The Tathagata does not exist after death' or 'The Tathagata both exists and does not exist after death' or 'The Tathagata neither exists nor does not exist after death' doesn't occur.

"For one who doesn't love feeling...

"For one who doesn't love perception...

"For one who doesn't love fabrication...

"For one who doesn't love consciousness, who isn't fond of consciousness, who doesn't cherish consciousness, who knows & sees, as it actually is present, the cessation of consciousness, the thought, 'The Tathagata exists after death' or 'The Tathagata does not exist after death' or 'The Tathagata both exists and does not exist after death' or 'The Tathagata neither exists nor does not exist after death' doesn't occur.

"This is the cause, this is the reason, why that has not been declared by the Blessed One."

(ii. Becoming)

"But, my friend, would there another line of reasoning, in line with which that has not been declared by the Blessed One?"

"There would, my friend. "For one who loves becoming, who is fond of becoming, who cherishes becoming, who does not know or see, as it actually is present, the cessation of becoming, there occurs the thought, 'The Tathagata exists after death' or 'The Tathagata does not exist after death' or 'The Tathagata both exists and does not exist after death' or 'The Tathagata neither exists nor does not exist after death.'

"But for one who doesn't love becoming, who isn't fond of becoming, who doesn't cherish becoming, who knows & sees, as it actually is present, the cessation of becoming, the thought, 'The Tathagata exists after death' or 'The Tathagata does not exist after death' or 'The Tathagata both exists and does not exist after death' or 'The Tathagata neither exists nor does not exist after death' doesn't occur.

"This, too, is a line of reasoning in line with which that has not been declared by the Blessed One."