To play on the League Public Beta Environment, your account must be Honor Level Three—well, not anymore.
Riot has lowered the Honor Level requirement from three to two so players can actually play Rise of Elements on the PBE, according to Richard Henkel, the Teamfight Tactics product lead. Level Two is the default level of all new accounts, so if you’ve never played League, don’t worry.
Honor increases when teammates commend you at the end of a League game. So if your teammates think you were fun to play with or just generally not toxic, you should be able to get your Level Two to Level Three.
Rise of the Elements is a massive change to TFT that encourages players to use champions with the same element to unlock trait bonuses.