My reinforced metal armour is really damaged i want to repair it can someone tell me how to?

You can repair it with similar armour, like metal amour or reinforced one. When you get the repairing perk, you can repair it with many different items. Example, after I got the perk, I can repair my Power Armour with metal armours.

Like Thelast said, if you keep boosting your Repair skill and/or get the Jury Rigging perk you can use similar items to fix weapons and apparel.
Also, there are several NPCs who will repair your equipment for a fee. I mainly go to Major Knight at the Mojave Outpost HQ. If you have the Confirmed Bachelor perk, you can talk him in to doing repairs for free and he repairs to a pretty decent level.

you can do this by picking up the same item which will allow you to repair it or by visiting vendors who repairs items for high amount of caps