Back to Square One is a Normal Spell Card.
Spell Cards are usually activated from the hand on your turn unless their type gives another timing window.
On the current TCG and OCG Forbidden & Limited lists tracked here, Back to Square One is Unlimited.
YGOPRODeck lists Back to Square One for these formats: GOAT, OCG GOAT, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Back to Square One appears in Dark Revelation Volume 3 (DR3-EN104) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Back to Square One is about $0.13 on Cardmarket (prices change frequently).
