There are TWO sides of the story here.
First, The Site-Admin needs to enable the option globally through Theme Options > User Dashboard as shown in the image below.
Once you enable Resurva or TimeKit or both the Booking Systems then there is nothing to be done by the Site-Admin.
Secondly, whatever needs to be done now, is the business listing owner from his own Dashboard.
You can have help how to create a Resurva booking widget
Then you need to get your booking widget URL
go to user frontend dashboard and see left side a tab Booking > Resurva
insert your Resurva URL and assign to any listing.
You can find Resurva or Timekit in Listingpro.