I had an umbilical hernia repair 6 weeks ago. I'm a bodybuilder. When I can back to lifting heavy weights?

First of all, congratulations on your hernia repair, jasiiu26!
It takes around two weeks for your surgical wound to heal after getting a hernia repair, but that doesn’t mean that the deeper tissues and underlying muscles have completely healed as well. It may take months for those to heal, so I suggest avoiding heavy weight lifting for at least three months to allow your abdominal walls to heal and avoid any increase in intraabdominal pressure.
However, you can start conditioning yourself by doing light cardio exercises around 10 days after surgery, and then start light weight training two weeks later. The increase in training intensity should be gradual.
Consult with your board-certified plastic surgeon so that he can properly evaluate your condition and give you a more personalized recovery plan.
Good luck!