How to register a property that was built 60 years ago

Please can someone advise how my in-laws register a property that my father-in-law built 60 or so years ago and they have lived in ever since.  The house is not showing on the land registry.

Do they need a solicitor/conveyancer, or is there a form that they can complete themselves?

Many thanks.

Lisa

Lisa - our PG1 explains how to voluntarily apply to register land/property for the first time. Whilst you don't need to use a conveyancer do have a read through the PG guidance and then decide
First registrations (PG1) - GOV.UK