How to start/force compaction on an Index

From the Couchbase Console, Settings->Auto Compaction->Index Fragmentation is set to 15%. However, I have indexes that have over 70% fragmentation, and they have been like that for a couple of days.

From the Couchbase Console I can force compaction on a bucket or view, but I do not see how to start/force compaction for an index?
Also if there is a CLI to start the compaction on an index, that would be fine as well?