As admin, you can generate a new team code for your team at any time.
To do this:
Open the Team tab.
Tap Team settings.
Select Generate new team code.
A new team code will be created immediately. Anyone joining your team after this point will need to use the new code. All those already in the team will not be affected.
You can also lock your team to prevent new members from joining. When you’re ready to welcome new members again, simply unlock the team and share your current team code.