Samsung Galaxy S7 No Signal,data,or service

[Android Central Question]

Hi, so I bought a GSM factory unlocked Samsung Galaxy S7 and my carrier is metroPCS. I know I need to adjust the APN settings and when I do still no signal or service. What am I'missing doing wrong and can you guys please put step by step or a video I kinda vet confused easily. Also I had my MetroPCS SIM before they changed to Metro by T-mobile if that changes anything.