You should just need to click the 'Find Team' button and your team will be restored. There can only be one team at a time per device so just note the team password of any new team you created, then delete that new team and then you'll see the 'Find Team' button. You can delete the current team from the in-game options menu. If your team does not appear in the Find Team menu you can select Import Team to enter your team password and restore your team.

Unfortunately if you are unable to restore your team and you have not recorded your team password it is not possible to recover your team. Please make sure to record your team password in the future.