Typically, the fastest way to re-use the same teams from one event to the next is to copy the event.
However, if the majority of teams are different, then it might be faster to add the new teams via the bulk team entry feature and then add the existing teams via their team dashboard page.
Go to the teams dashboard
Click into a team
Select the event and division in the add to event section and click the green + button:
That's it. The team has been added to the event.