Accounts wont let me sign in or change password. Please help!

I am trying to change the microsoft main alias on a different account so I can change it to this email because I dont use the other one and its just a hastle to remember the password and sign in. It's currently logged in for my XBox and i want to change the email/alias so its more secure and i can have everything connected through one account

Whenever i try to add this account/email as an alias to my other account it says "This email address is already taken. Please try another." So when i try to enter a personal google email it allowed me to add it, however i cant create an account. I have never used the personal google account for microsoft before, and it sent me a confirmation email i went to create an account with that email and it says it already exists and i need to sign in. However, when I go to sign in it says my account doesnt exist or my email isnt linked to anything.

I would prefer to use the one connected to my phone that already has a microsoft account as my new alias but if that isnt possible how can i fix the "existing, non-existing" account issue

:)