My fitbit glass cracked after a fall with my mountain bike. can it be replace? if so where must i take it for repairs

most likly replaced

Check to see if the connection point on both pieces are intact. Make sure the band is the right size for your device. If all else fails try a new band. As for the cracked screen, is it still under warranty ? If not the cost of repair will come out of your pocket. The do make screen protectors for all devices. It's in your best interest to purchase one.

Use this link for instructions.It is best if you have your bike on a bike stand. If you don't have a bike stand then you can put it upside down with a towel under it. Make sure that none of the wires are being pinched while either in the stand or while upside down.
http://www.parktool.com/blog/repair-help/rear-derailler-adjustments-derailleur

http://www.parktool.com/blog/repair-help/categories/derailleur-systems

1) Replace the chain.
2) Adjust the travel of the front and rear derailer.
3) Make sure the rear wheel is set properly in the rear fork.

did it stop working while it was in the shop or a day or two later?

if it broke in the shop it would fall into the duty of care to your vehicle. kick up a fuss if you havnt already paid for it. but if you have, goodluck getting any money back from a dealer.,

Most body shop can replace and paint the new part, but aviator, explores, mountaineer all do that, must be a ford defect.