Go to the Marketplace in the outpost, click the arrow to get to "Services - Repair", look at your armor and find out the level of engineer that you need to repair it.
Scroll down to find the appropriate level engineer, all engineer's cost money depending on what they charge. Generally, engineer's become more expensive as you level up, especially around the 40+ zone.
Drag the armor over the engineer's Wrench icon, then confirm if you want it repaired, the armor will be restored to maximum condition and the fee will be taken out of your inventory.
Note: You must have the money required on hand, it cannot be directly taken from your Storage.