Hey!

If you are a PCMB student, you must be familiar enough with biology. But before changing stream, you must consider that the paper patterns of JEE and NEET are very different. so be prepared for it. As you were preparing for JEE, your physics must be better than most of the NEET aspirants. So, that is a plus point. For Biology, its mostly from NCERT, so be thorough with that. Also solve as many previous year papers as possible.

Best of Luck!