Click the green "Subscribe" button on the workshop page

Bring up Chivalry's old launcher by right clicking Chivalry in your library, and click "Launcher (SDK, Workshop, Safe mode)"
Now, click the button in the lower right corner of the launcher window.

Launch Chivalry, and go to "Create game" It will bring up this window
Click "User Created Maps" and scroll to find the map you downloaded. The in-game name of the map is always at the bottom of the description on the workshop page, under "Maps Included:"
Use the bot option to set how many bots you want.
Now you can click "Start offline game"

If you're playing a star wars map, then you may want to download the lasersword mod:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=691189495
And select it under "Mods" when you're creating a bot match.