I am trying to create a trigger that will fire off a email to a user when the assign to person completes their activity.

how do i add a email template to this trigger below?

trigger Trigger_Request_CompletedAfterInsertAfterUpdate on Task (after insert, after update)
 {
    
 
   Task[] completedTasks = Trigger.new;
   for(Task t : completedTasks){
      if(t.RecordTypeId == '01270000000UGMe' && t.Status=='Completed'){
         Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
        
      }
   }
}