Can't Import Presets to LRC

To build on Johan's reply: If the preset files end in ".lrtemplate", they are old-format presets and you can't use the menu command File > Import Develop Profiles And Presets to import them (due to a LR bug).

Instead, in the Presets panel in Develop, click the "+" button in the upper-right corner and do Import Presets.

If the preset files end in ".xmp", open one of them in Notepad. Copy/paste is contents here. That will let us figure out how to proceed.

What file extension do these presets have? Is it .lrtemplate perhaps? In that case you have received the presets in the old, pre LrC 7.2 format. Lightroom Classic can convert them to the new .xmp format (and I can tell you how in another reply if needed), but I think a preset author should provide you with the correct format in the first place. Another possibility is that these are profiles, not presets...