kubanoba, "Move User" feature is not currently supported by Zimbra. I opened the bug 39937 to deal with this issue. In the meantime, please feel free to use the following workaround to move user A from BES1 to BES2:
- add user A using BB manager on BES2
- reset activation password for user A on BES2
- enterprise activate BB device
To flip user A back from BES2 to BES1:
- reset activation password for user A on BES1
- enterprise activate BB device
To view/open the bug, please use
Bugzilla Main Page. In addition, please keep an eye on bug 39937 for the update on the progress with this issue.