If you deleted the cfg you created/downloaded (in case you didn't, do it), just open your game and write into the console "exec default.cfg". This will create a default cfg and you can play with the default cfg. In this case, i recommand to close the game, create a backup of the default cfg you created and if you want, reinstall all the cfg that you want to try.

This method is a bit harder than the one above. Just go into your CS 1.6 Steam folder, so C:\Progam Files\Steam\steamapps\common\Half-Life\cstrike and delete the configuration which you created/modified/downloaded. So go into the game and write into the console "writecfg". The game will create a new cfg named "(null)". So, close the game, go another time into C:\Program Files\Steam\steamapps\common\Half-Life\cstrike, rename the "(null)" cfg into "config", create a backup folder and put the default cfg into this one. So, if you want, download and install all the configurations you want. In case you don't like the configurations you downloaded and installed, just open the backup folder and reinstall the default cfg.