Hi and welcome to The Tortoise Table. First of all, well done for rehoming this little tortoise, and it sounds to me like he will have a good life with you.
Regarding feeding, I think because of his blindness, you do want to try and incorporate a scent with his food, and cucumber is a good one. You don't actually have to feed lots of the cucumber itself, because you can squeeze some of the juice from the cucumber onto the food and that should be enough -- but it won't hurt him to have some cucumber as well, as it will help to keep him hydrated (but you obviously don't want too much cucumber because it doesn't have much nourishment).
When you tried to hand feed him, did you brush the food you were holding against his mouth to show him there was food there? I've had a look on some forums and several people with blind tortoises either hand fed at the beginning, or had a special dish where they sat the tortoise right next to a pile of food that they had sort of semi-liquidised (so he doesn't have to aim for a thin leaf at the start, but has a mass of food he can go for). You are already sort of doing that by putting him on the plate with the food, and I think that as he gets older and used to walking around, he will find the plate of food himself (probably good to keep it in the same place as tortoises have very good memories and once he has found it he will remember where it is).
I think the undershot beak could be more of a problem than the blindness, so a trip to a vet is a good idea (do make sure that it is a qualified reptile/exotics vet, and not an ordinary vet). In case you don't have one already, here's a link to our list of recommended vets in the UK
https://www.thetortoisetable.org.uk/tor ... s-by-area/ , and if you can't find one near you, let us know and we'll have a look.
It's not essential, but personally I think I would change the coir to another type of substrate, as coir can get very dusty and isn't the best texture for tortoises to live on. We recommend a sandy soil substrate, mixing ordinary screened or sterilised topsoil that you can buyin bags with children's play sand (about 60% or 70% soil to 30% or 40% play sand usually works well, and you can spray it every day or two to keep it from getting dusty). The other disadvantage of coir is that if you have a bulb blow, and hot pieces of glass fall on the substrate (rare, but it does happen), then the coir can catch fire, and we know of at least one case where that happened.
Hopefully others will come on with some ideas for encouraging him to eat, but good luck and please let us know how you get on (and if you have a photo of him we'd love to see it, as we never get tired of looking at photos of tortoises.
Nina