Hey ZekeXZayah,
This message just means that whichever EA account you're trying to use has already been linked to a different Xbox account. You are not able to link two separate Xbox accounts to the same EA account, even if you remove the first.
In that case, you would need to link this Xbox account to an EA account that's never been linked to Xbox before. You can check out more information on linking here, or if you're trying to make other changes to an EA account and are running into any issues, please contact support directly so they can see what other options may be available.