Hold page to activate your structure scan pane while in split screen, hit menu and you should have a drop down and be able to select what type of scan you want to see (left, right, left+right, down. etc…)
I run one of my HDS 10’s almost always in that screen mode. Beleive I go to sonar main page then chose sonar + Imaging and chooose down. My units are in my boat covered in heated storage so I can’t actually look at menus right now, but can tell you that’s one of my favorite screens combinations. Have set up in one of my hot keys now.