How to unlock iphone 5s T-Mobile?

I bought a T-Mobile iPhone 5s from someone on CL. The phone was on contract, now it won't pick up signal when I inserted SIM. How to get this phone unlocked?

THe phone has been reported stolen and thus it has bad IMEI. You need to get it fixed and unlock the phone to use with other carriers. If you need help with getting your T-Mobile iPhone 5S factory unlocked, mail me.

I would return it

I actually had tmobile - I had to pay off the entire phone before they would unlock it but they did it for me after interrogating me.

You need to get it unlocked for use with other carriers like Simple Mobile or GoSmart.