I am from south india. so, we discovered covid vaccine. now the virus can change its shape and enter our body again? that means we have to find another covid vaccine? what people here are saying is 'this is the second wave'. could there be a third?

Forget “what people are saying” - mostly massive disinformation. Yes, coronavirus can “change its shape” (called “variants”). The vast majority of these variants are still prevented by coronavirus vaccine (at least Pfizer, J&J and Moderna. - Maybe a LITTLE less so for Astra-Zeneca and Sinopharm). All still pretty effective Try to find a reputable doctor to ask about what you got - hard

If available, get vaccinated, and try to obtain a legitimate vaccine, such as listed by Dr Lentek.