One of the most important things to do is to build up the musclr to support it. Do alot of ground work. Raised trotting pols etc gymnastics. On a long rein so that they work from behind and bring their back up
There are many varying levels of severity when it comes to kissing spine so I really couldn't say 100% since I don't know your horses case personally but one of the horses I ride has kissing spine and it barely affects him at all. He jumps a 10 every time, always looks comfortable, and is a wonderful mover you would never know. I think it also depends on which vertebrae in particular are affected. We also encourage him to use his back as much as possible and build a strong topline which I think really helps. The only thing the horse I ride has problem with is dismounting. Getting on is no problem, you can even get on from the ground and you couldn't do anything while riding to bother him but the vertebrae that are affected are right under the points of the saddle that touch his back so dismounting can make him squeal so we found a particular way that made him comfortable. I think you can expect to see a full recovery in your horse (but again I don't know the particular case and am not a vet) and wish you the best!
It greatly depends on the location and the severity of kissing spine but also on the tolerance of your horse to these lesions. Faced with the same lesion, not all horses are equal.
In any case, only your veterinarian who has observed your horse in consultation and who has seen the radios allowing the diagnosis of these lesions can give you an objective opinion on the adapted treatments as well as the possibilities of healing of your horse. And not to mention healing, he will be able to give you very useful indications on the way to work your horse with his lesions and on the sporting level to which he will be able to work.
Hoping that you and your veterinarian will find a solution to best relieve your horse.