How to edit/place a simple scheduling code inside site/404 page

Hi,

New here.  I seem to have always been able to edit my site and now I'm having trouble.  I want to just update changes to prices and also need to figure out where to place code to connect the book button with schedule.  When I go there and click to edit, it says in a black box to put in safe mode. I click on that and then click the pencil icon toedit and it shows box that a code is in...however, I don't think that is where I put the code (which by the way I havenot touched...so not sure why this is showing up).  Full Slate is the online scheduling system I use and I have contacted them also.  

Thank you for any suggestions.

This is normal behaviour for a code block running scripts. Double-click on the block and edit the code.

Are you trying to update what's already in the code block, or add a new one?