How to configure Router that attach to switch

my work place recently make a network that attach all the computer in the facility to a wired network using switch. 5 computer attach to 1 switch. 1 of the port at switch is attach with router. how to configure router so that other computer that not attach using wire can go online.

my network is :

ISP—MODEM–SWITCH—COM 1
—COM 2
—ROUTER
—COM 3
thank you