Enfield Town FC uses the 3G Pitch in Donkey Lane, adjacent to the QEII Stadium, primarily for senior team training asa well as for disability teams, walking football and football schools run by Enfield Town FC Community Sports Development Ltd.
The 3G Pitch facilities, and nearby Playing Fields, are adminstered by the London Borough of Enfield, who can be contacted at https://new.enfield.gov.uk/services/leisure-and-culture/sports-facilities/
The 3G facilities are directly ahead of you as you come down Donkey Lane. Proceed into the main car park and the 3G facilitirs and Playing Fields are accessible from there.
The nearest toilets are in the building in the middle of the playing fields. If you are at an Enfield Town FC event, then the organisers may have had the stadium toilets opened for you.