After you do your initial sync, you can sync a new team by going to the Settings and selecting 'Sync League/Account'.
From there you can see an existing list of accounts and what operator they are with. If you have additional accounts you can select the operator and sign in.
From here, you can select an existing account and chose the teams you would like to sync. Select the team(s), hit sync and you'll be directed back to the lineup page where you can use the drop down to chose the team you want.