I know only pi bonds can change and sigma must be in the same place..
“H2C=Br….” (4 dots on Br)
use the energy conservation principle
Please use resonance rule. So H2-C^+-Br. In words, you will have two hydrogen atoms bonded to Carbon atom, Br bonded to C. In this structure, Carbon atom will have + charge, as formal charge, and Br and H2 will have neutral charge. Please you use formal charge rule. I hope this help.