On the far left side of the console view click the icon with the two triangles that are opposing each other (both facing center).
And your Inserts / Sends will re-appear.
Here's a video done on the topic of sends in Studio One 3.
I strongly suggest watching our video tutorial series that will walk your around the interface to show you where all the buttons are. Joe Gilder started this series on Studio One 2 and continued it with Studio One 3, 100 videos in total.