You cannot currently repair guns in ROB RUN. The practical solution for an unusable firearm is replacement: find another gun in city loot or buy one through the Black Market at Lenny’s Motel or your base laptop. This is the current Early Access situation, not a promise about every future update.
Replace the gun through the Black Market
Visit Lenny’s Black Market or use an installed Black Market laptop at your base. Look for a replacement you can actually purchase and afford, rather than a repair service for the gun already in your bag.
Some firearms have Shipments progression requirements. If a desired weapon is unavailable, inspect its unlock conditions before setting aside the purchase money. Unlocking an item and buying the item are separate actions, so budget for the complete replacement route.
Choose a usable loadout rather than spending everything on the most expensive available firearm. Leave enough money for supporting supplies and another outing if you lose the new gun. A cheaper replacement that keeps you playing may be more useful than a purchase that empties your reserve.
Find a replacement while looting
City loot is the other replacement route. Inspect a weapon you find before selling it or leaving it behind, particularly if your current gun is no longer usable. Keep the replacement tied to the activity you are preparing for and the space available in your inventory.
Do not plan the outing around restoring the old gun at a hidden workstation. Until a firearm repair system is available, another usable weapon is the action that resolves the problem.
Separate gun repairs from armor plates
Replacement armor plates replenish depleted armor protection. They can be dragged onto your character or used through quick slots, but this is not a firearm repair action. Vehicle repair tools also serve a different purpose.
The existence of either item does not establish that a gun repair kit exists. Read the item’s intended use before buying it, and avoid spending resources on a tool meant for another piece of equipment.
Before leaving for your next run, confirm the replacement gun is usable, check the supplies your loadout needs, and keep enough reserve to recover from a failed outing. Those checks address the immediate equipment problem while the game has no functioning gun repair route.