@IC_Sentry In the Teams client you can select what Sign-In address to sign in with, but it have to be the correct one. What SIP-address or Sign-In address you have is decided by your Office365 administrator. Normally the Teams Sign-In address and your E-mail address is the same but they can be different.
@Linus CansbyI am the owner/administrator. Editing my profile, I don't see that as an option, just upload a picture . When I go to the Team tab, I don't see setting a SIP-address or Sign-In address as an option either for anyone.