How to cure "if I blamed someone who we should not blame"?

this is my own thinking and not from any sutta, why not become a noble follower yourself? Fighting fire with fire. Then Dhamma of the noble followers will come to you naturally. Example, if someone causes you some displeasure, you have the knowledge that pleasure/displeasure is not caused by others but because of Phassa (contact), vedana arises. This is not a common knowledge. all other beings in the universe who have not heard dharma think that pleasures or displeasure caused by others, by self, no cause...etc.

when one applies Pratītyasamutpāda to everyday life, there is really no one to blame. Clinging to 5 skandha as self is Dukkha

It is the intention behind the criticism that will determine the weight of one's kamma. So check youself everytime, what you do, say, and think to the other person, whether they're for sincere positive, and constructive criticism for their own good, or it's simply for the sheer unwholesome pleasure of criticism. The safest approach, is to thoroughly investigate and gather all the info. before saying anything to anyone. Refer to MN 58 for some guideline on proper speech.

In Buddhism, everything is forgivable.

If a noble person is practising their realisation, there are no grounds for us to blame them since the noble person will not be harming us.

If a noble person unintentionally harms us, they should ask for our forgiveness & we should forgive them.

If we think a person that intentionally harms us is a "noble person", we are mistaken because a noble person cannot intentionally harm others, even out of good-will (e.g., to kill a murderer) because the eightfold path prohibits all violence for any reason.

It is common for ordinary people to mistakenly believe practitioners of forms of black magic are noble people.

That is why if a monk kills any human being for any reason, including mercy killing, they are expelled from the monastic order.

AN 9.7 says:

...an arahant monk whose mental fermentations are ended, who has reached fulfillment, done the task, laid down the burden, attained the true goal, totally destroyed the fetter of becoming, and who is released through right gnosis, cannot possibly transgress these nine principles.

[1] It is impossible for a monk whose mental fermentations are ended to intentionally deprive a living being of life.

[2] It is impossible for a monk whose mental fermentations are ended to take, in the manner of stealing, what is not given.

[3] It is impossible for a monk whose mental fermentations are ended to engage in sexual intercourse.

[4] It is impossible for a monk whose mental fermentations are ended to tell a conscious lie.

[5] It is impossible for a monk whose mental fermentations are ended to consume stored-up sensual things as he did before, when he was a householder.

[6] It is impossible for a monk whose mental fermentations are ended to follow a bias based on desire.

[7] It is impossible for a monk whose mental fermentations are ended to follow a bias based on aversion.

[8] It is impossible for a monk whose mental fermentations are ended to follow a bias based on fear.

[9] It is impossible for a monk whose mental fermentations are ended to follow a bias based on delusion.

There's no completely escaping the consequences of a bad deed unless the Karma becomes defunct. But you can do much to mitigate the effects.

1. If the monk is alive, apologize in person. If he is dead, think of him and apologize.
2. Do good deeds. ex: offering alms to the monk you insulted or to the Sagha as a whole.
3. Do meditation. ex: Spreading Metta to all beings, practicing the four foundations of mindfulness etc.

All of the above will help a great deal, but only a Buddha would know what exactly you should do to make a Karma defunct, if it is possible.