Can't set character on gamemode

Hello,
I tried building everything and it still doesn’t work. Is there anyway you can explain a little bit more about right clicking to see the combo box. I don’t know what you mean (sorry). Could it be that my version is super buggy or like my computer. How about having a big map? I don’t know if that would make a difference. Thank you for helping. I hope you could solve my problem.

-c0mbatcat