They need to send you the fhp file after they have exported the preset you've made for them - they are usually named "username_10.fhp" and can be found in the preset folder.
Once you've gotten that file you need to put it in your FeralHeart ---> presets folder. Or if you are using the Preset Sync you can simply ask them to upload the preset to the sync, and you should be able to see it as well.
Make sure you've created the preset in the same format as you have in the preset.material txt file. If you saved it in a png format you need to make sure it says .png in the text file too (and not jpg or the other way around)