Declare Squall and Fear of Missing Out as attackers.
Fear of Missing Out's second ability triggers, untapping Squall and causing you to get an additional combat phase after this one.
Holding priority, activate Viscera Seer by sacrificing Fear of Missing Out.
Deal combat damage to an opponent using Squall, triggering Squall's second ability, returning Fear of Missing Out from your graveyard to the battlefield.
When Fear of Missing Out enters the battlefield, its first ability triggers, causing you to rummage.