If the device bricked during a software update, you would either need to try a master reset with the hardware buttons if possible, or it would require a warranty exchange assuming it still qualifies
Have you been able to try a reset?
...and THIS is the reason manufacturers prefer OTAs.
(and the reason I hold my breath any time I do a BIOS update on a computer).
Stores can't unbrick (specifically according to their rules, if they try, they could make it better or worse, and if it gets worse, they don't want to be the ones responsible).
There's a "chance" you can find information on xda on how to unbrick. This is completely unsupported by T-Mobile and I'm not going to recommend it because instructions could be interpreted as vague for someone who isn't familiar with the processes (they DID save me with an older device, but I was anxious at every step about making it worse, but my case I was ready for a new phone anyway and in the financial position to buy one).
If you have the warranty exchange, you'll get a refurbished device (note this as part of your decision making). You'll also potentially be responsible if there's other damage located on your device or if they've been able to determine you voided your warranty in any other fashion (like rooting).
I've had that happen on my phone before. What I did was turn off my phone, connect the USB cord to a USB 2.0 port on my PC, then hold the volume up button while connecting it to the PC. Don't let go of the volume up button. You will see a "download mode", after that it will take you to a "firmware update" screen. You can let go of the volume up. If you were updating your phone through PC, set your phone on a spot were the cable doesn't disconnect. Follow whatever instructions you needed to do. If it fails, you can take off the battery and try again, but just be mindful for whatever it is you are doing.