You can setup an automation rule under Admin > Workflows > Automations > Time triggers > New rule to delete the tickets in your account.
In tickets > if Source > is > select all the sources you use
Delete the ticket
Note: Make sure to Turn OFF the rule once all the tickets have been deleted.
Please note that the Time Trigger rule can perform actions on the tickets which were created or updated in the last 30 days. Tickets which were inactive beyond 30 days will not be impacted by this rule.