Reassinging one bone from the rig


I have a problem with rigging. So I have this character I made and now I’m doing the rig. I used automatic weights and the rig worked perfectly. After that for some reason I changed one vertex group and now it does not work that well. I have tried to use weight painting but it is like shooting in the dark to get it work that well again.
I don’t want to start all over again because my rig is pretty complex.

BTW it is a hand bone so I have perfectly working vertex group on the other side. But I could not figure out how I could duplicate that and rename the vertex groups.

So my question is: Is it possible to reparent with automatic weight only with one bone of the rig?
Other solutions are of course appreciated.

sry for my bad English. I hope you understood what is my problem

I got it fixed. I separated the right hand and mirrored it. After that I changed the names of the vertex groups to correspond the left hand bones.