Unauthorized Sellers on My Private Label Product: Legal Insights and Next Steps

Hello all, I recently posted how someone tried to list my branded snack products under their listings. Based off the responses I received I was told to enroll in brand registry at the soonest. Being a startup, this is a bit costly on my end and wanted to ask you two things:

Have you enrolled yourself into Brand Registry without a lawyers assistance? For those who have been through this, is it possible to use your own personal lawyer for the brand registry issue? My personal lawyer hasn’t dealt with Amazon’s Brand Registry before, but he is well-versed in intellectual property law. Would Amazon accept this, or do they require that we use lawyers from their IP Accelerator program?
I would greatly appreciate any advice or experiences you can share