Ensure it is not inside a ZIP or RAR archive. If it is, extract it so you have the raw .fifamod file ready. Run FIFAModManager.exe as an Administrator.
Once imported, the mod will appear in the list on the left. it or click Apply Mod(s) to move it to the "Applied Mods" list on the right. Download File Messi 2011 FaceMod By ViP3eR.fifamod
Locate your downloaded Messi 2011 FaceMod By ViP3eR.fifamod file. Ensure it is not inside a ZIP or RAR archive