I'm having some difficulty reconciling yr mention of implementing HACCP in combination with the GMP scenario you describe. It's no accident that GMP is a PRP for HACCP.
Frankly, if an employee is not capable of self-deducing the objective of wearing a hair net i fear you are facing a fairly solid "brick wall".
I also find it difficult to comprehend how yr visiting EHO is seemingly perfectly OK with the existing arrangement. Perhaps it's actually the "norm" for the food category which you somehow slot into ? if so, perhaps you are seeking the impossible.
However I assume you are the "QA" for this "facility" and have been sourced to attempt to convert it into something which an EHO can qualify as complying with basic GMP requirements ??
I have encountered a possibly analogous scenario with respect to seafood raw material suppliers who perform limited pre-processing operations and had traditionally been somewhat under the radar but times had changed. I found the only pragmatic solution was to generate a "stripped-down", officially acceptable, GMP checklist for the Production Supervisor of such a team who then had to interpret/implement the list so as to be appropriate within an "on-site" context. Easy to say, not easy to do, unless there is a specific driving motivation. Does the latter exist in yr situation ?
IMEX local Fishery-related Commercial Organisation often have shareable videos depicting basic GMP requirements as you refer and as per the refs I previously noted. I daresay a long, long established Industry like Seafood in the UK has similar. Failing such, IIRC, various older threads here reference US-oriented equivalent downloadable items. You may have to do a modicum of searching, eg via -