Re-edit submitted PDFs

I had my students complete an assignment using Kami. I added my comments and returned in Google Classroom, but some students scored poorly and I want them to revise the assignment. They are telling me they are unable to re-open this assignment in Kami to do any further edits. Is there an option to edit an assignment/file multiple times after submission? If so, how? If not, can that be added?

I think I am having a similar problem (see my post). Is there a support forum for paying customers that is a bit more active? I was hoping for a response.