Is there a decent app that can measure if you are missing any frequencies?
Yep, but you'll need a calibrated measurement mic. If you don't have one,
you can buy one here.
The software is
Room EQ Wizard.
Here's a tutorial. If you plan to order the UMIK-1, you've got time to read and familiarize yourself with the tutorial. The UMIK-1 ships by steam boat from China.
If you're looking for an Android app,
AudioTool is pretty neat (also available through the
Amazon App Store), although not nearly as useful as REW on a PC, and you'll have to find another way to generate tone sweeps (Audacity, YouTube videos, whatever. Google has no shortage of links to sine sweeps).