I can add links to other JIRA tickets when I create a new ticket, but if I try to add a link to an existing ticket, the field isn't being displayed (not hidden either). I've tried the "Link Issue" button, but it only lists Confluence and Web Link (see below). I want to add a JIRA link???

In a past company using JIRA, there was an "Edit" button that allowed me to add/update any field like new.