The altimeter on my Timex Helix reads LO and can't be changed. I changed the battery -- anything else I can try?

Timex Helix ABT.
This watch calculates altitude by measuring air pressure and relating that value to the international standard atmosphere. 1013.25 mb = 0 metres.
The Timex ABT does not display negative altitude values. So if the measured air pressure is greater than 1013.25 mb and the altimeter is reset (select altimeter, pull out the crown 1 click and press and hold the lower left button) the watch will display LO. You can experiment with this. Wait till the barometer reads 1013 or 1012 and reset the altimeter. The watch will display zero or maybe 5 metres. Or wait till the pressure goes up to, say, 1022 and reset the altimeter. The watch will read LO again. If this happens alot, you probably live fairly close to sea level. What you can do to trick the watch is use a vacuum cleaner to raise the perceived altitude of the watch then calibrate the altimeter (pull out and rotate the crown) and change the altimeter reading to, say, 200 metres. It wont read LO then. Keep an eye on it and the atmospheric pressure. If the pressure starts to rise then adjust the altimeter accordingly. Remember this watch is designed to measure proper altitudes where the air pressure isnt likely to be as high as 1013.25. If you are mooching around near sea level the naturally changing air pressure will often make the watch read LO.
If you live up in Montana at 1500 metres (ISA standard pressure about 840 mb) all the time then the watch will always read a positive value and you can calibrate it from reference to a map or road sign etc. The atmospheric pressure will unlikely reach as high as 1013 up there and the watch wont read LO.