Roof repair special leaking issue, need help

[Beary Bowles]

So I've own a 11 unit apartment building in Missouri.  This is the season when it rains constantly during the month of April.  Luckily enough when I bought the property I had a 5 year roof warranty.  Mind you the roof is flat and have a total of 4 corner drainage spots.  I've had one particular tenant call several times about water coming into her unit (which is near corner drainage spots).  I've called the roofing company and they have came out to the property multiply times.  Recently I've found out that the drainage spot might not be running into the drainage valves and into the units from inside the roof.  What can I do to remedy a solution? 

1: rip up the existing roof near drainage corner

2: already fixed and sealed rain runoff drainage pans.