Multisite subdomain - re SSL certificate set up

HI there, I have set up a multisite (I use 1and1 for hosting) and I have bought an SSL certificate for one of the domains set up within the multisite (theoldfarmhouse.com which is this subdomain: theoldfarmhousenew.myaccommodation.website Please can you tell me what I need to do to get the ssl certificate to show - I don't know what to do with the domain mapping to get this to work! I tried to use the https option for domain mapping and it just whirled and wouldn't set.
Many thanks for your help!