In your web admin, go to Settings > Web-admin settings
Enable "Add Time - Legacy Mode"
Once this has been enabled, you should be able to add or remove time to an account.
Go back to the dashboard then search for the user and click on the 3 dots (···) beside the username, and select add/remove time.
Add or Remove the desired amount of time in this window.
NOTE: The cost price will be based on the default price per hour in Financial configuration. Removing time can only be used if time has been manually added to an account. It doesn't work with time offers that has been added to the account.