was https hosting, changed to forwarding, cert issue

Hi all,

domain was hosted, used https with lets encrypt cert.
owner did management contract with other company. They ask to redirect the domain to their site.

After i switched hosting type from hosting to forwarding and visit the domain (using https), instead of forwarding, it shows as certificate error. [Which does make sense as the proper domain cert isn't available anymore, it now reverts to the servers own security cert.]

How to overcome this issue?

cheers,
Tom