There is 2 ways to update your client mod The first and easiest way is to unsubscribe and resubscribe
Open the steam workshop and search open world Click the "subscribed" button to unsubscribe
Then click "subscribe" to resubscribe again
Now the mod should be updated
However sometimes this doesnt work
To fix this open your steam library and find rimworld
Right click "rimworld" and click "properties"
Click "local files" and then "verify integrity of game files"
This will begin to verify the game files and update any and all mods. This can take a few minutes
Once that is done you should be good to start playing again