How to Install and Enable Icon Xaero's Resource Pack for Xaero's Maps
Placing the Pack Correctly
Icon Xaero's Resource Pack is a resource pack, not a mod, so it belongs in your resourcepacks folder rather than your mods folder. Open your Minecraft instance directory, locate the resourcepacks folder, and drop the pack file inside. If you are using a launcher that manages instances separately, make sure you are in the correct instance's folder before copying anything over.
Activating It In-Game
Launch the game and go to Options → Resource Packs. Find Icon Xaero's Resource Pack in the left column and move it to the right column so it is active. Resource packs stack, so place it above any other pack that also touches Xaero's map textures to make sure these icons win. Click Done and let the game reload.
Confirming the Icons Appear
Open your Xaero's Minimap or World Map. Waypoints, structure markers, and entity dots should now use the pack's custom artwork instead of the defaults. If nothing changed, check that the pack is actually enabled, that it sits high enough in the load order, and that you are looking at a map type the pack covers. Some icons only show for mods you actually have installed, so missing icons for absent mods is expected behavior.