you don't say which program you are using

if you are using one of the versions that allows you to expand down to object level in the page and layer gallery you can do it there

otherwise if you right click on a blank area of the page there should be an 'unlock all on page' option that will do it, but you will need to relock anything else you want to stay locked on the page afterward

or you could click the 'all layers/objects editable' button in the page and layer gallery and cut the rectangle, unclick the button and paste the rectangle back in place...