Cannot uninstall or install Avast AV

[Charles50]

I'm running High Sierra on a Mac Pro 2012. I'm trying to reinstall Avast, unsuccessfully.
On macOS, all I should need to do is move the app to the Trash. There were other files that needed to be deleted and I deleted those, such as plists and those in the Application Support folder.
When I try to install again, the message tells me it cannot and I need to uninstall the previous version first. Instructions tell me I must open the app and select Uninstall from there. And I can't run the app coz it's gone.
So I'm stuck in AV limbo. How do I either complete the uninstall, or override the installer's inability to continue?

[DavidR]

Check the Avast MAC Security sub-forum there may be a related topic.

https://forum.avast.com/index.php?board=5.0

Sorry I can't help being a Avast for Windows user.