In my Bitbucket repository I have clicked on branches, then clicked the 3 dots on the right of branch-B and click Merge. However when the new dialog box pops up, it says:
Source: branch-B
Destination: master
Commit message: Merged branch-B into master
And doesn't allow me to change the destination. What I want to do instead is to merge branch-B to branch-A. How can I do this on Bitbucket?