Syntero

Go inside, walk to the right hand side of the receptionist booth without even saying anything. Go all the way down the hallway on the right and turn right. You will pass the normal gendered restrooms, keep going. The hallway bends to the left a little but keep going straight. At the end of the hallway, turn left. When you get to the seating area there, turn left and the single-person unisex restroom will be on the left under the restroom sign.

This is a therapist/psychiatrist place. I imagine You're supposed to be a client but they won't say anything... and if they do, I imagine they'll be sympathetic if you explain You're trans and need to use the restroom.