1) Go to Online Store → Actions → Edit Code
In forder "Layout" find file "theme.liquid" and delete 2 lines of the code that connects the snippet in "theme.liquid":
<!-- Snippet for Simple Preorder app --> {% include 'simple-preorder-bootstrap' %}
2) In folder "Snippets" find file "simple-preorder-bootstrap.liquid" and delete it.
If this does not work, please write to support@kad.systems