Just a little "Pinch"

This image shows what is going wrong with the Rigify Rig on my character. There is obvious pinching on the character’s right knee. I was think about finding a way to fix the problem. The most effective method to fix it was to copy the bone weight on the left lower thigh and paste it to the right lower thigh and then mirror it. But I forgot how it is done. Please jog my memory.

Do I have to go into Edit mode for that method?