Guest Purchase, but can't print return shipping label

[m.marco.w1cfdqdaxm]

I ordered a piano from a company through ebay as a guest, but I have to return it as it's not fully functional. The seller is paying for the return, so I clicked the link to print the return shipping label and it takes me to a log in page. I type in my guest login code, but it's making me register for an actual account. I can't just log in as a guest anymore. And what I bought as a guest won't show up on my actual account so I can't print my shipping label... How am I able to print it??