I got a similar looking one, similar form, and you use the forward back button to change /set the FM output on the transmitter, then you tune the FM to the same frequency - but it has a numerical read out on the front (which we can not see if yours has in the photo). I think the middle button (call button on mine) acts as a toggle of there is an extra CH button, maybe that did it. I did not read any institution, it was fairly intuitive.
What I also had to do was find spot on the FM range and that took about 3 tries to get one with the least amount of background hiss or interference from some other more powerful transmitters (radio stations).
I actually cam on here to ask a different question about similar bluetooth fm transmitter.
A bluetooth device like this connected to an iPhone, and the iPhone is connected to the net, over say 4G network - Is there a chance these bluetooth devices can piggy back out over the net and connect with home and thus send data back to the manufactuer?
I have seen this with ethernet based or woof based security cameras, but I realise it might be possible with Bluetooth, but I am not sure. I can not monitor the in and out connection on my iPhone like I could with a network router to see where devices are reaching out too.
Any ideas? Maybe I'll start a new thread.