Contacts app, deleting several groups

A user has many identical groups in his CONTACTS app. Hundreds of them. Does anybody know of an efficient way how to delete them, except one of each “type”.

Does exporting all contacts, emptying all contacts and then re-importing bring the groups back, or only the contacts?

iMac High Sierra 10.13.6

On my iPad I have an App called Delete Contacts. I just took a screen shot of the first screen when I open the App. It is easy to use and deletes multiple contacts.

Doesn’t the Contact app on the make have a find duplicates, or are there too many for that to manage. As I remember, it wants to Merge the duplicates into one, and that may not be what you want.

It"s not about duplicate contacts (well, yes, we have that too, but it’s easy to solve).
It is about multiple GROUPS.
Groups cannot be generated or deleted at all in iOS.
We have to work in macOS (High Sierra 10.13.6)