Upvote:1
You can make a fresh application right now and ask that it be forward-dated up to 90 days from the issue date. You need to select the start date such that it does not result in your having two visas that run concurrently (or they will refuse).
It needs to be a fresh application because there are no provisions for a visitor visa to be extended. Also, remember that the business visa was abolished last April so you need to apply for a Visitor (standard) visa.
Note that they do not generally like to issue back-to-back visitor visas unless you have a long history of performance, so you should take extra care in explaining why it's necessary. Alternatively, consider applying for a longer validity visitor visa if you qualify, the form gives options for 6 months, 2 years, 5 years and 10 years. If they decide you do not qualify, they will issue a 6 month visa anyway and keep the difference in price, so be sure you qualify...
You also wrote later...
The problem is that last time when I applied for the Visa I was not able to travel as the place I was to travel had a fire accident and my meetings were cancelled and that's why I just had the Visa but never travelled on it. Now I need to travel that place again in August and therefore I need a Visa for it.
None of that changes this answer. Next time please edit the question rather than provide a new answer.