DSO201 Nano test signal problem

Hi there!
How can I use test signal? I found a socket for oscilloscope probe connection, USB socket and that’s it! No socket to use test signal!
How it can be? I imagined that I can use both devices to repair my home audio system so it seems to me that I bought unused thing!
Please help me!
Thank you in advance.

There is lanyard eyelet on the corner. That’s the signal out.

Thank you very much for your rapid response:)
It is, but Seedstudio Manual for DSO Nano v1.0b says that it is “50 Hz Square Wave”. The same Manual says that device has “test signal, Built-in 10Hz -1MHz (1-2-5 Step)”
If “50 Hz Square Wave” and “test signal” are the same thing - how to change the frequency of the signal, in general how to control signal parameters?
Thank you very much again:)

First it is highly recommend you upgrade to Benf firmware then use FR menu to control the frequency.

Thank you very much, maybe you meant FO menu?