How to edit items on the backer portal?

Can someone tell me how to edit the number of items on the order page? Either there are no keys to do it or I am too stupid to see them, and if it is some esoteric method, I am unable to divine it.

Hello, Gwydion. Please send a letter with a detailed description of your problem to team@owlcatgames.com. Don’t forget to specify the e-mail used for your order. We’ll check it for you.

Thank you, my problem has meanwhile been solved by support (they edited it).