H1 B Multiple approved pettition

I have transfered my H1 B work permit from Employer A to two different employers (Employer B and C at the same time) Employer C pettition was approved a week before Employer B and both the pettions were got approved and they are valid now,

I have accepted offers from both B and C and decided to work for employer C. I’m currently with employer C for more than a month and received my first paystub also. I have now changed my mind to work for employer B.

Can I Join employer B now after having worked for employer C for more than a month? Do I need to notify USCIS about this change? Please help me answer this question.