I'm afraid you're on your own. T-Mobile does not sell parts or offer repair services. Those are 3rd party services that you'll have to look into.
Hey melissawass! I'm so sorry to hear about your phone's cracked screen - I've been there. To be honest, the warranty doesn't cover physical damage, so really you'd need to add insurance back when you purchased the device in order to cover screen damage. There are definitely third party phone repair services you can look into - I think there are four shops that do this within a ten block radius of my home here in my city. Another option you might pursue is to contact Samsung directly and see if they offer a repair service and if so, do a cost comparison. If Samsung offers repair services and the costs are similar, it may be worth having the screen repaired by them so that your phone's warranty stays intact (the manufacturer's warranty is good for one year from the purchase date), because replacing the screen through another party may void that warranty. I'm sorry we can't be of more assistance ourselves, but I hope you and your fingers are safe and that we're at least able to point you to some possible solutions!
You may be on your on. You are not alone, There are thousands of us! I asked a question on here if there was a known issue with the S7 Edge screen cracking. The answer I got was the opinion of the man that answered my question. So he did answer my question as far of his knowledge at the time. I have done some checking on my own. And the S7 Edge uses the gorilla glass 3. The new Samsung products are using the gorilla glass 4. The Gorilla Glass 3 is not an inferior product to the gorilla glass 4. A Samsung representative online chat told me that the Gorilla Glass 3 is the better of the two as far as hardness. The gorilla glass 4 will be more flexible. Even a T-Mobile rep told me that they are hearing more about Samsung s7 Edge glass breaking even inside the best phone cases. My opinion is based on facts and it is the the glass is far too rigid and normal flexing of the phone snaps the glass. A defective pairing of the glass to the phone. This is not the first time Samsung paired something wrong, of course I'm speaking of the Note 7 battery too large for the device.
Your friend with a cracked screen Samsung Galaxy S7 Edge for no apparent reason when it cracked I thought there was a hair on the screen going from one side to the other until I wiped it off.