We either actively transferred the scouts out of the den to their new troops in Scoutbook, or just ended their memberships if they weren’t going to a troop. @jacobfetzer already covered the process to either allow the council registrar to transfer the scouts (i.e. submit transfer application and wait), or to actively end their pack membership. To actively transfer a scout, the easiest way is generally to coordinate with the troop(s) to which the scouts are moving, and have them use the transfer tool in their roster (My Dashboard -> My Units -> Unit Roster -> Transfer in Scout) to move the scout to their unit.
As @jacobfetzer noted, make sure everything is closed out with the pack before transferring the scouts, as it could require transferring them back to fix something you miss (e.g. payment log balance, awards not marked Leader Approved or Awarded).
IIRC is an internet acronym: If I Recall Correctly.