U3415W, how to connect a new computer?

Hi,

I was allowed to borrow a person's office for a few days. I would like to use my own laptop, keyboard/mouse, but I would like to connect to the screen which is u3415w. I have my own HDMI cable, and that slot in the monitor is not taken. However, when I connect my laptop, I cannot see how I can change the source from DP to HDMI? Usually there is a menu button, but here there are 4 black dots in the bottom of the screen - when I touch them, a picture of a lock appears on the screen. Removing the DP cable did not help either, and the monitor did not switch to HDMI. This is very confusing for me - is there a menu button somewhere, and if not, how can I change the source?

Thanks!