Was not allowed to edit an instance of an instance group during the lab. The edit button was grayed out.

Yup, this is a two+ year old video and it looks like that functionality was dropped. Click on your Instance Template > click Create Similar > add the network tag there > save. Go back to the Instance group > edit your Instance Group > change the template to the new template you just created > save. Under the Instance Group click on Rolling Restart/Replace at the top of the screen > choose the "Replace" radio button and click the blue "Replace" button. Wait for it to finish swapping out the servers and for the new ones to come online. SSH should work after that.