on first join:
set {predefined::*} to 1, 2. and 3
set {_gen} to random object out of {predefined::*}
if {_gen} is =1:
execute console command "/luckperms user %player% parent set team-1"
if {_gen} is =2:
execute console command "/luckperms user %player% parent set team-2"
else::
execute console command "/luckperms user %player% parent set team-3"