You need the right terminology Professional Boxing Trainer or a Coach.

It's just like any other Governmental licensing requirement. You fill up the required forms and submit the required documents to verify the relevant experience along with the fee. Each commission is going to have varied requirements so it depends on what jurisdiction you are applying.

Nevada's looks simple:
http://nevadaathletictrainers.nv.gov...pplication.pdf
California looks more complicated:
http://www.dca.ca.gov/csac/forms_pubs/athleteapppkg.pdf