If both players reveal the same location/battlefield in game 1, do they have to change it?

Ruling: No, if both players in a 1v1 choose the same named battlefield, both players continue play with those battlefields. There is no rule requiring players to change duplicate locations.

Nuances:

• The confusion may stem from the 2v2 format rule, where you and your ally cannot use the same battlefield
• Players also must have three different battlefields in their battlefield deck (not duplicates within one player's deck)
• In casual play, a player may voluntarily switch for variety, but they are not obligated to do so