Did you just make a new weapon or armor set with custom icons but it reverts to the original item icon in your inventory? This is how to fix it:
How to make it use your custom icon
Open the PrimalItemWeapon_YourWeaponBP / PrimalItemArmor_YourArmorBP, scroll to the icon section & remove the material from "Item Icon Material Parent".
How to make it use your custom colored icon
If your new weapon or armor is setup for colorization and you want the colorization to show up on the icon like the default Ark weapons & armor do, you will first need to make a copy of your icon and export it to your preferred graphics design program such as Photoshop.
Once exported, go ahead and color the areas of the icon to reflect the colorization areas on your weapons main material.
Re-import the new colored icon texture then make a copy of the "Item Icon Material Parent" material for your weapon/armor. (usually something like "HUD_Colorize_Weapon/ArmorName").
Next, change the "Basecolor" & "ColorizationMask" to yours.
Finally, link the new material to the primal item.
Please see the following link for more information on Ark's material colorization setup. Colorization - Ark DevKit