I googled "forklift" and it appears to be an FTP client for macOS.
File names in an FTP client can either be names of files that are on a remote server, or names of files that have been downloaded into a folder on your local drive after being downloaded. If the former, I don't think there's any chance KM can do what you want here, because the files have to be downloaded first before the action you are using can manipulate/move them. But if the latter, there may be a chance. We may have to delve into AppleScript using your app. Since I don't have forklift, I can't delve.
I'm not an admin on this website, but I recommend that an admin migrate this question to another thread, because it's not really a question about Michael's macro. It's a question about getting similar functionality for a specific program.
So in my opinion the best way to deal with your question is to find out if Forklift has support/hooks for AppleScript. If it does, then AppleScript can probably obtain the names of the selected files and allow you to process them in a KM AppleScript action.
However there is an alternative. If you can precisely document a mouse and keyboard solution to your problem, we could get KM to use its mouse and keyboard actions to solve the problem without AppleScript. That's usually very tricky and sometimes has lower reliability. Personally, I love this approach, but since I don't have that app, I can't even start with it.
If you open the macOS app called Script Editor and use that app to open the Forklift app, you can browse its support for AppleScript. If you see properties with names something like "List of Selected Files" then that's a good clue that it supports AppleScript.
Fair enough. But now that you mention you can do it with dragging and dropping, my earlier point may merit more muster, when I said, "If you can precisely document a mouse and keyboard solution to your problem, we could get KM to use its mouse and keyboard actions to solve the problem without AppleScript." In other words, if you can precisely describe how you do it with the GUI, it's probably possible to do the same thing with KM which can use the same GUI.