Where is the user manual?

My screen showed me the message "no cable connected" when I plugged in the HDMI.
I tried a multitude of manipulation so that the screen is recognized, in vain ...
Finally, I found on the site of amazon uk it was enough to repeatedly press the "enter" button on the side to change the screen input source ... But why do -this indicated anywhere, either on manual (too short) or on the screen (by calling the "input" button rather than "enter").
In short, I did.
The screen is of good quality.
It is not expensive compared to its size and the presence of an HDMI input.
Only the instruction fails ... but ... it's not insurmountable! Just a waste of time!