IIRC, that is an entry-level series monitor (so it has few ports). You might be able to buy an cheap-dongle and use the VGA-Port for one of the computers. If you are set on HDMI, you could try an small/inexpensive HDMI-SwitchBox (like used in Home Theater setups). 
How do you connect a ThinkPad laptop to a Dell S2318H/S2318HX monitor with only one HDMI port?  I'm using a Dell Inspiron 3668 tower, if that helps.
Connecting Laptop to Desktop PC with only one HDMI port