Trouble to link front page and back page

I created a page on the backend and want to link with one parenting page that appears on the frontend.
On the SiteOrigin image windget where it has the destination URL I usually choose on the side bar on the right the page I have created on the backend. However…it is not showing anypages anymore. It just shows the posts and listings. what can I do to make pages appear on my sidebar again. I have tried to put the URL copying and paste from the back page, however it doesn’t work it once I log out from Admin, on the front page it takes me to login page not to the page I wanted originally to link.
Does it makes sense?
Thank you in advance.
Regards
Florence