Dell S2421H User Manual page 16

You can use the dropdown list to switch to any input source.
NOTE: DDM communicates with your display even when the display is displaying
video from another computer. You can install DDM on the computer you frequently
use and control input switching from it. You may also install DDM on other
computers connected to the display.
16 | Managing Multiple Video Inputs
HDMI1 (Active)
HDMI2
HDMI2
HDMI1
S2421H
HDMI1 (Active)
HDMI2
HDMI2
HDMI1
S2721H
Dell S2421H
HDMI2
HDMI1
HDMI2
Dell S2721H
HDMI2
HDMI1
HDMI2