Changing your Password restrictions or Prevent use of breachable passwords settings will not result in your existing users being forced to change their current passwords. Only new or changed passwords will have the new requirements enforced. To find these settings, type "Password restrictions" in the search bar at the top of every page and click on the matching result.

To require a user to change their password, you can enable the Require password change on next login setting for the user. Type "Manage users" in the search box at the top of every page and then click the matching result. Edit the user and click on the Authentication tab to access the Require password change on next login setting.