See a GP if you’re having problems with your hearing. They will check your ears for wax and will refer you to a hearing specialist for an assessment if they think you might need a hearing aid.
You can have your hearing assessment at a number of locations, including some local opticians, but you need to be referred by your GP. They will ask you your preferred location when referring you.
NHS hearing assessments are overseen by East Sussex Healthcare NHS Trust Audiology Team. You can find useful information on their website https://www.esht.nhs.uk/service/audiology/
There is other useful information regarding hearing assessments and aids on nhs.uk including advice on getting a hearing assessment and hearing aid privately.