I am a new player and I have an electro-acoustic Fender Newporter guitar. This guitar is from what they call their California series and they are all equipped with a built-in preamp with a tuner from Fishman. It looks like this:

I only play acoustically for now, I don't have an amp or anything. I have a regular tuner, but I was wondering if this on-board tuner can be used to tune the guitar when playing acoustically? I wasn't able to figure out how to turn it on. I guess it only comes on when the guitar is connected to an amp? Since I don't have one, I can't verify this.
Does anyone have a guitar from this series or know about them to be able to tell me whether the tuner can be used when the guitar is unplugged?