If your RCA RCT6603 phone is corrupt or bricked. Download RCA RCT6603 stock firmware from here. To get it back to a working condition again. 

All you have to do is simply download the below-given RCA RCT6603 firmware files and tools on your PC. And then follow the given instruction to install the Stock ROM on RCA RCT6603 using SP Flash Tool. This guide is also helpful to unroot. Or fix any software malfunctioning problem.