Gamertag not changing?

Hey there! I just recently bought the Xbox Game Pass for PC to be able to play Sea of Thieves on my computer, and upon downloading it the first time, my gamertag in the game was the wrong gamertag, so I created an entirely new account, got the Xbox Game Pass on there instead and refunded the old account's game pass, and upon uninstalling and reinstalling Sea of Thieves, my gamertag is still the old tag despite making an entirely new account with an entirely new gamertag? How can I fix this?