Extending an account will allow a Guest to add more devices/time than he/she paid for. This might be necessary for customer support.
Below are the steps that will help you do that.
Navigate to the Accounts tab on the left and use the search bar to find the account you want to extend.
Once you have found the right account, click on it to go into the account's details.
Find the most recent transaction the Guest has done and click on the three dots next to it to find the extend option.
In the next screen, you will be able to extend the time and increase the number of devices allowed.