- Head on over to the Workbench from Juan and interact with it.
- Go into the highlighted Supremo section.
- Once there, select the Exterminador, the Assault Supremo.
- Look to either of the open Gadget Mods slots.
- Select either one to see the options for Gadgets that you can add beyond the pre-installed pair, Molotov and Baseball.
- You are likely to have a number of options that can be installed here: Perception Grenade, Dynamite, Grenade, Throwing Knife, and Smoke Grenade.
- Craft whichever fits to your playstyle best.
- Exit the Workbench having made a mod for the Exterminador to finish this operation.
Use the workbench to building a Gadget