If you have a customer contact you who wishes to be removed from your marketing email database, you can easily remove them by using the 'customer search' setting.
In the screen shot below, you can located the customer search on the left hand side of the settings under 'customers' title.
Once selected, it will bring up the customer search section where you can search your database via; email, phone or name.
When a customer match appears, you will be able to clearly see if they had opted in for marketing with the clickable 'YES' text.
When you click the 'YES', a box will appear at the top of the page to confirm if you wish to remove the customer and opt out from future marketing. See the example screen shot below.
After you have selected this, you will then see that the customer has now been 'opted out'. See the example below of a customer that has been 'opted out'.
You can always then opt the customer back in if they request via the individual booking place, next to their email address contact.