Hi,
Have been using JIRA/Confluence Cloud and Mercurial on separate server
We have just moved to Bitbucket Cloud and linked to JIRA that is working ok.
Within an a JIRA issue, there is an option to create a "Branch" in Bitbucket. This appears to work fine for new branches moving forward and that it displays the link to the branch from within the JIRA issue.
How can you link an existing JIRA issue to an existing branch in Bitbucket so that within the JIRA issue it displays the link. Within the issue it only has the option to create a new branch, not link to an existing Branch.

Have search forums and have not come across an answer for this.
If this has been answered somewhere, can you show me the answer?
Thanks in advance