Background
Long time ago I have, unfortunately, created an embarrassing Facebook group and later decided to remove it. According to Facebook's instructions, that can be done by removing all members and then removing myself. The group disappeared. Now, after about 4 years, it turns out that four members were deactivating their accounts at the time of the deletion and the group has magically appeared again. Unfortunately, my only association with that group is two (very, very) embarrassing posts and I'm trying to delete them.
Question
Is there any way to delete own post from an open group of which I'm not a member anymore? (Using Facebook UI, Graph API, a contact form, anything, any method)