GS305E How do I share my ethernet service with a second computer?

Current internet service from Spectrum using Cisco DPC3008 cable moden ethernet output to Google Mesh Net router.  Etherneet cable from router to iMac.  Works fine.  Trying to add a second iMac to internet service using GS305E Smart Switch. Connected cable modem ethernet output to one port of GS305E.  Connected Google Mesh Net router to second port of SG305E.  Connected second Mac etnernet cable to third port to GS305E.  The second Mac assigns the default IP address and does not connect to internet.  I tried to use Netgear SDT tool.  It requested I setup a new WiFi network.  I set up the new network using existing credentials for my local Google Mesh Net.  Now I apparently have multiple WifFI networks.  SDT can not any deivices on this new network.  I tried deletiing the new network but stilll could not configure the switch for shared internet.  I'm stuck.  How do I configure the switch?