Mayfair. Have a look inside.
Unscrew the milled side screw at one end. Unscrew the 6 endplate screws at that end in rotation a little at a time and lift the end off carefully with screws still in situ. You will immediately have access to the reeds/reedbanks. If each reed is screwed down to the brass shoe with 2 screws you have the much more upmarket model which I have. If the reeds are all together in banks pinned and waxed down you have the cheaper accordeon type.

Before you take it to a shop or repairer I would recommend having a word with someone who has done their own repairs or knows something about concertinas in general and let them have a good look at your box, perhaps even take it apart. It may be that if not much needs doing to it they could do it for you.

If you tell us where you live we can perhaps recommend somebody local to you.

Repairing the levers, springs, pads, bushes is much more fiddly but if only a couple need attention there are plenty of players/amateur repairers around. The big problem with professionals is they are inundated with work and have long waiting lists.