how to change glass face on 20 + years old women's Gruen wrist watch?

You must have missed the myriad results when you did a search to help yourself. Maybe your browser sin't working properly

I found a few sites inside 30 seconds.

The work won't be stunningly cheap, but there are plenty o foutfits out there who would replace a crystal for you - even if it needed custom trimming/making.

Here's a few I found:

http://www.crystalfit.co.uk/

DIY - but you need to source a crystal: http://forums.watchuseek.com/f365/diy-guide-how-change-your-own-watch-crystals-174080.html

http://handycrowd.com/how-to/personal-stuff/replace-broken-crystal-on-rolex-watch/

http://www.watchrepairshop.co.uk/watch-glass-replacement/

http://www.clockparts-uk.co.uk/contents/en-us/d133.html

XXXXX
October 2015