If you've rescued the milk farm, it should just be an option you can select when choosing to renovate!
I have and it doesn't work. Its from a game that I made before the update, I'd but that might be why. Also I renovated cassie's basement before the update too
i think you have to go to the milk farm and check out the new room to the left before the option opens up
I see no room to the left
Hmm, should be a room to the last! Are you playing the latest release?
Though, there's apparently some bugs with renovators at the moment, so I probably need to look at it again