Simply use CastXMR. It already has support for Cryptonight V7. It was initially developed for AMD RX VEGAs but it can now be used with AMD GPUs. Not sure about what hashrate your rx 550s will do on this but my rx 470s do 800-850 h/s. Not bad at all good sir.

Here is the link to CastXMR: https://bitcointalk.org/index.php?topic=2256917.0;all