I hate when that happens, but it’s been good after microsoft help screwed up my computer and I had to do a wipe and clean install. So if that is not working for you, the only other option I have for you is to create a new xbox account. Back when Xbox was first out, (I don’t play gaming systems very often,) and you had to have a microsoft or hotmail account. They also had family plans back then, so we used my hotmail account and my brother used it and I was able to create one for my daughter. When they did away with the family plans, my brother was able to create an account using his yahoo email address. So he plays under both my hotmail and his yahoo. He starts the game with my hotmail account then he clicks on the profile and swaps to his yahoo account. If you truly want to start over that would be the best way to do it.
I just looked at the folder and not finding player information in there. I did however find it at
C:\Users<user name>\Games\Age of Empires DE\Users<xbox gamertag>\Config
I would suspect you would have to delete all of those, but definitely the .uh file. Let me know if that works please.