The “Meta” section is not editable. Just remove that widget and put your own in its place instead.
Okay but surely the code for it is somewhere?
Yes, but you’d have to edit the core code, which would be not very useful in the long run. You’re better off using a Text widget and putting whatever links you want into that widget instead.
Look for the widget.php file in wp-includes. You will need to change it again possibly when wordpress is updated to new version though.
For a quicker easier solution try installing widget called quick-admin-links. This gives you the ability to have a link to create a new post or page right from meta widget which I find is extremely useful.
