Hi
i am not an expert in this particular case but i followed theses below steps . here are they.....

Unscrew the case back with a case back tool (aka Jaxa wrench) which engages
the notches in the case back. I'm assuming the watch has a screw back - if
it has notches it does. Pop out the old battery.

In some watches you have to
unscrew a clip but in most the battery pops right out. Examine movement for
evidence of battery leakage or other damage. Carefully clear away any crud
at the edge of the case - the tiniest metal shaving will short out the coil.
Install new battery of same type. Handle new battery with non-metal tweezers
or rubber gloves, never bare fingers. Inspect case back gasket or preferably
just replace it with new o-ring of same size. Gasket should be lubricated
with silicone grease. Reinstall case back using wrench. If you are
concerned with water resistance the watch needs to be tested in a pressure
test machine. I'm sure the pros have more tips but this should suffice for a
Timex where it would not be a big loss to damage or break the watch.

i hope you can successfully replace the battery
thank you