Slots won't drag from builder to landing page

Hi everyone,
I’m learning to create my first Mautic landing page.
The slots won’t drag from the builder to the landing page.
I have tried clearing the cache in CPanel, which was suggested in another post - hasn’t helped.
Can anyone help, please?
Lizzy

When I try to drag, as the cursor and text box icon crosses over to the left where the theme is, they disappear and it’s like the cursor is still navigating the right hand side of the page and can’t go over to the left