unable to edit link

We have a page https://www.jigsawbox.com/webinar/one-time-offer that has the words ‘No thanks, I’m ok for now’ hyperlinked to https://www.jigsawbox.com/webinar/the-jigsawbox-advantage-jsb-3

I need to change this link, but when editing, I click the link button, which does not display the current link, paste in the new link and it directs me to here https://www.jigsawbox.com/webinar/wp-admin/edit.php every time, without allowing me to save any changes.

Please help!