Sometimes, a customer may not reply to the support response in time, and the ticket may be closed due to inactivity. If you wish to reopen a closed ticket when the customer replies, you can enable the default automation rule ‘Automatically reopen tickets when the customer responds’ under Ticket Updates automation.
You can also edit the rule to customize the rule according to your business requirement.
Here is a video demonstration on how to reopen closed tickets when customer responds, explaining the above scenario.
Please reach out to firstname.lastname@example.org if you require further assistance in setting up the automation rule.