How do I replace the battery on a blus fossil watch BQ-9101340207?

hi donna.
not sure if this link will help you out but have a look.
What battery number should get for my fossil blue BQ 9140 Google Search

If you pull out the battery it will have replacement numbers on the battery itself.

Approx. Case Diameter 42.71mm x 44.67mm crown included

To find a registered repair person in your area.
GOTO:
http://www.watch-clock-makers.org/
Hope this tip helps.
r/ David
http://antiqueclock.clockstop.com/

Most watch backs either screw off with a special case opener that every wachmaker uses or pried off with a knife like case opener or sometimes a knife. Take this to your local watchmaker for battery replacement. Batteries are readily available but are a bit tricky to install properly and are best installed by a qualified watchmaker.