its been so long I have forgotten everything about bot matches. On quake 2 GOG version I can start an eraser bot game but how do I add bots and change maps?

This should help:
https://www.quakewiki.net/archives/emporium.planetquake.gamespy.com/eraser.html

Specifically, this part:
To run the game, type the following from the DOS Shell command line, whilst inside your Quake2 folder:

quake2 +set game eraser +map (please read below to find out which maps are supported)

The from within the game, type "bot_num X" to spawn X number of bots.
If you do not see any bots in the game, then I advise you to read the Frequently Asked Questions near the end of this file.