I have 2 issues that talk about the same problem in Bitbucket.
How do I merge them or close one to point it to the other?
The easiest way would be to close the duplicates, and cite the original issue.
closing #4 as duplicate, see #2
'closing' and 'see' are keywords that automatically change '#4' and '#2' to links for those issues.
You can do this in a commit message or when you resolve the issue in the Issue Tracker.
More information here: Available commands