See the following discussion thread:
https://groups.google.com/d/topic/dspace-tech/PDrxOwkJIQI/discussion
The thread is a bit dated, but is shows that this function is not supported in either the UI or the command line tools.
Here is some code that I run to perform this operation. You need to force the discovery index and the OAI index to be aware of the changes after you perform a move.
Fortunately, since you are running DSpace 6, you can trigger the re-index of a specific community/collection from the command line.
usage: org.dspace.discovery.IndexClient [-cbhf] | [-r <handle>] | [-i
<handle>] or nothing to
update/clean an existing index.
-b (re)build index, wiping out current one if
it exists
-c clean existing index removing any
documents that no longer exist in the db
-f if updating existing index, force each
handle to be reindexed even if uptodate
-h print this help message
-i <handle to add or update> add or update an Item, Collection or
Community based on its handle
-o optimize search core
-r <handle to remove> remove an Item, Collection or Community
from index based on its handle
-s Rebuild the spellchecker, can be combined
with -b and -f.