Is it possible to change a customer's password?

We would always advise that customer's reset their own passwords by using the reset password functionality available. See the following FAQ:

https://ptaevents.freshdesk.com/support/solutions/articles/17000093929-i-ve-forgotten-my-login-details-how-can-i-change-my-password-

However, administrators have access to change customer's passwords. To do this browse to "Admin" > "Reports" > "Customers" and use the search form to search for the customer. When you have found the customer, click the ID of the customer to access their account view.

Once in their account view you can change the customer password.