I assume your ATPL A and H were both issued by UK? I think you would need to do training as determined by an ATO to renew a rating (it'll be the whole course given how long it's been). Then the update to a UK Part FCL will happen as part of the rating application process. You will have to do training as required and an IR test (with an IRE) to get your IR back (bridging from your ATPL.A) -
but basically go to an ATO for the type you want to fly.