How do I find out which team includes operator X...

Select the Operator group and press the delete key (PC) or Fn-backspace (Mac) - this will clear the Operator group. Then clear the operator in a similar fashion and type in the name of the operator you wish to use.

The Operator group will then only display their operator group(s). If they belong to only a single group, that will be filled in automatically, otherwise you may select from only their operator groups.