I presently have a multi device subscription but only use on one device How do I change to a single device subscription?
First, I’m an Avast user and not an Avast Team member.
You could start here Home | Official Avast Support select relevant option and follow it through. Or here https://support.avast.com/support/tickets/new > use the I need help using a product option, and the attach file in new window to submit the file.
The Second link would seem to be a good start point - select the Account and Billing then Account Billing, followed by, Select a reason. This would seem to be a reasonable start point - at the bottom of that list there is a Get Support option. I don’t know where that would take you (Chat or Telephone option possibly, I don’t know), as an Avast Free user I haven’t been down that track.