Once you meet a certain person, (won't say who because of spoilers) you will have him at your camp and he will introduce you to the crafting table. The achievement is cleared by simply swapping mods on gear. You can easily use your leather mats for attire and iron for weapons to do this right away, or naturally clear the achievement by swapping mods that fit your needs.
To do this, select the gear or weapon while at the crafting table. On the right hand side select mod gear. Choose a mod from any of the tiers and select slot 1 or 2. In early game there is probably only one slot. Make sure you apply it by using your materials on the left underneath the gear or weapon you selected.