You can only use 1 "Exchange of Night and Day" effect per turn, and only once that turn. You can activate 1 of these effects;

?Send 1 LIGHT Warrior-Type monster from your hand to the Graveyard, then add 1 DARK Warrior-Type monster from your Deck to your hand, with the same Level the sent monster had in your hand.

?Send 1 DARK Warrior-Type monster from your hand to the Graveyard, then add 1 LIGHT Warrior-Type monster from your Deck to your hand, with the same Level the sent monster had in your hand.