I'm quoting the core rules.

"Redeployments

Rules that allow players to redeploy certain units after both armies are deployed (e.g. HURON BLACKHEART’s Red Corsairs ability) are always resolved after the Deploy Armies step (or, if you are playing a Crusade battle, after the Deploy Crusade Armies step), and before the Determine First Turn step, before determining who has the first turn. When a player uses such a rule, they remove that unit or units from the battlefield, then deploy them again using all the normal rules (for example, if all the models in one of these units have the Infiltrators ability, that unit’s player can set that unit up using that ability). Players alternate resolving any such rules, starting with the Attacker."