Go to
https://www.gov.uk/government/public...ing-for-medals
and apply. You will need his Service Certificate. If you haven't got it you can apply at
https://www.gov.uk/get-copy-military...-elses-records
I have used the first one to get a medal which I didn't know I was entitled to. Not difficult but it takes a few weeks to get the results.
It's all on Google - you only have to ask...