According to dmvroofs.com check out these steps:
Step 1) If your roof is fairly new – call the roofing company that installed your roof and have them fix it.
Step 2) If it is an older roof, or the original installer will not fix it for some reason, you have three options:
Fix the roof yourself
Have a roof repair performed by a roofing contractor specializing in flat roofs
Or if your roof is near the end of its life, it is best to replace it rather than throw any more money away on repairing it.
Step 3) To prevent more damages to your roof, interior of your home, or the inventory and the equipment of your business, it is a good idea to put up a tarp on your roof, until you choose a course of action – either fixing it yourself or choosing a roofing contractor to repair or replace it.
Step 4) Estimate the real cost to a repair flat roof. Learn what is involved, what the hidden costs and fees are, and why we consider flat roof repair to be “sunk cost”. This comparison will help you decide if it is time to finally replace your flat roof, or if repair is a feasible option.