App.OnStart
Set(varUser,User())
Set(varTeam,Lookup(Admin,varUser.Email=Email).TeamName)
This two variable will store current user's info and current user's team name.
In your gallery item code:
If(IsBlank(varTeam),ref,Filter(ref,TeamName=varTeam);
This code will first check if variable varTeam is empty or not. If it is empty meaning user is not in the admin list. And will see all the record. If it's not empty meaning user is in the admin list and will filter ref list according to current user's team
Tweak it according to your need