ovs-ofctl del-group <bridge> [group_id=<id>]

Delete group in <bridge>. If the group_id is specified, the group that <group_id> in <bridge> will delete, otherwise, all groups in <bridge> will be cleared.
Example:

admin@PicOS-OVS$ovs-ofctl del-groups br0 group_id=2
admin@PicOS-OVS$ovs-ofctl del-groups br0