Auto update a Master branch from another branch

Hi,

I am new to gitlab and I am trying to set up a relationship between two branches. Master_2.6.1 and Master_Season-5. Whatever changes in Master_2.6.1 needs to automatically be applied to Master_Season-5. And Im looking at all the different things online and I am confused how to do it.

Im not a master degree computer scientist I am just a casual coder who makes mods for games. So please use laymans instructions in a response :)

Still love Gitlab!!