Originally Posted by
CPH-Flyer
You can always change to UA number at the UA gate, but as domestic upgrades clear earlier, and good E+ seats may be gone, it would be probably be worth contacting United to check if they can manage that
It's not as easy as you think - I tried at MUC and it's impossible according to the gate agent. I tried again at IAD and the agent couldn't do it - I asked her if she could just remove my TK G, and she said it's impossible. After a while she said she had to switch to another system to get it changed.
Check the UA forum - I'm not the only one struggling with this problem.