It’s the managers responsibility to open up the regular registers. When incidents similar happen with me I just tell the customer sorry these are the registers available right now, would you like to talk my csm? Sometimes they say yes and they complain to the csm to open more register 9 times out of 10 it doesn’t happen and the customer has 3 options, leave their items and go home, use the self checkout or wait in line at a regular register.

Years ago i had a middle aged man with 3 small items bitching about how we had only one other register open and he was stuck using self checkout. I tryed multiple times to assist him, scan his items for him etc He always resisted and basically would scream at me, at one point he got in my face and said he would be shopping elsewhere, so I told him sir you can shop where ever you want, no one is making you shop here at Walmart. Well he got mad at me and was like your gonna get fired for that! Well in the end he ended up speaking to the CSM that was on duty and now here comes the best part. They both come back over to me and the CSMsays the customer would like to say something to you. Me: yes? Customer: I like to tell you I’m sorry for how i acted. I don’t remember what he said exactly but he did apologize to me left and that was the end of it.