There's no easy / quick way.
He'll need to apply for a mortgage in his own name, and bank to accept him. As the house is in your sole name, you'll need to effectively 'sell' the house to him. You'll both need to engage a solicitor to carry out conveyancing (his will complete what's required for bank), he'll pay stamp duty, and you'll pay capital gains tax (if there was a gain).
I don't know if there's anyway around it for example if you can show although you were legal owner sibling was beneficial owner and had been paying mortgage on their own.