Patience ... Which are you looking at, horizontal or vertical?
I switched to the horizontal ... Stick your finger under the silver lever until the water drips out into the "cup". They'll get curious & check it out. If you can get one going the rest will copy. Some say to remove the regular waterer, some prefer not to.
Main thing is to monitor, you could remove in the mornings & for peace of mind put the regular on in at night?
I only have 4BO so I use a hard plastic gallon container, drilled a small hole about an inch below the rim, recommended 1 nipple/4 chickens (I installed 2), I mark the level of the water (monitor), test the nipples every time I change out water. For some reason when I change the water they are waiting for me to "test" the nipples & drink what comes out. I know they're drinking on their own as the water level goes down.