How do I use Photo Finder All Features ?
I just purchased this, on line, but do not know how to use it.
MacBook Air 13″, macOS 10.15
You need to use the app developer resources for that. (Contact them - use their forums - read their documentation).
Bear in mind Apple says you should not use third party apps for duplicate removal, and this is not one of the ones regular contributors on this forum use and recommend.