Change user field when changing another field

Change user field when changing another field

Hi there!

I am trying to make a user field update when a user edits an open field, For example If I, Jhonny edited field A
I want field B to change automaticlly to Jhonny so I will know who changed field A without relying on the timeline becasue it doesn't document for more then 2 years of history..

Any ideas? Couldn't do it with workflow yet

Thanks in advance!