Use DR2MM, drop the file in your DR2MM installation folder, under the mods folder.
E.G.: X:\Games Folder\Diablo II - Resurrected\D2RMM 1.7.3\mods
Open up DR2MM, then refresh the mods list if the mod doesn't appear. The mod should appear as a data mod in the list with the associated warning that this is not a DR2MM mod and may conflict. Ignore the warning, but make sure the mod is lower down on the list. Click 'Install Mods' and then run D2R.
You should see the alternative appearance of the Paladin immediately during character creation (or if you already have a Paladin).