If you want to remove a value from list you should use remove and use the delete mutation if you want to delete like the complete customer in this case. I think when you check the generated mutations and queries definitions that will make it easy for you. So I’m attaching the screenshots from Insomnia (you could be using a different tool) to try/view queries or mutations.
I hope these will help you to view queries/mutations available to you.
Thanks for the typo mention. Btw here are the two posts I told you that were coming out soon.