Hi,
You can create a daily Automation and use a relative date compared to the date in your custom field to unsubscribe your users from a list.
Please have a look at the documentation: https://docs.acymailing.com/advanced/send-follow-up-messages-based-on-subscription. The example is for a series of follow-up mails, but it's pretty much the same. Instead of adding a mail to the queue you can unsubscribe your user.
If you need further assistance, please post your question and add a screenshot of the summary tab of your automation.