Add a second button next to the button with the link.
Attach a microflow tot this button that gets the current object as input parameter and opens a dialog with a text box in a dataview with the attribute that has the URL stored. Make sure that the obejct is refreshed on save else the underlying page could still show the old value in the button.
Another option could be to display the attribute in a text box on the screen and allow the user to edit from there. To save the change in the url add an on change action to the text box saving the object.