It’s probably going to be a PIA. I am not up on US regulations. I did the same thing in Canada. I had to get a Canadian certificate.
My understanding is the US will accept and recognize your seatime but not your certification.
So you will most likely have to do the whole shebang of mandatory BS courses at a regognized training facility. If you are lucky some UK course may be approved. You will need to look up list of approved foreign course providers.
First step get your discharge book, and watch keeping testimonials take them in to your local USCG examination office and fill out the sea time form. Detailing the whole lot.
They will take copies of your original certificates.
Apply for a US MM you got the time.
If you apply for a lesser certificate. You may find you are caught in a quandry. Getting your seatime approved and accepted may be a once only.
So get approved for the highest certification you can.
If you get approved for a lesser US certificate you may have to accrue seatime on this certificate prior to writing a higher one.
So get your seatime approved first.
Local guy might not know answers to what is required. You may have to apply to regional office.
Once you have seatime approved they will tell you which exams you are required to take.
Worst case scenario. All of them from 2nd Mate up.
They will take copies of all your original course certificates and tell you which ones you require be prepared it’s likley to be the whole lot.
So the remaining question. Is it worth your while.
You got MM there is a demand. Do you want shore side or seagoing.
Fortunately for me I used my DOT Cert in Canada to sail as a chief Mate prior to regulations changing So I only had to do the the Masters exams again. Plus all the Marine Emergency Duties, Electronic Nav RADAR First Aid etc.
There is more BS now like leadership etc. GMDSS is one of the few which might be acceptable.