This from : https://developers.google.com/games/services/common/concepts/leaderboards#leaderboard_time_frames
"The Google Play game services SDK automatically creates daily, weekly, and all-time versions of every leaderboard that you create. There's no need for you to create separate leaderboards for each time frame.
Daily leaderboards reset at midnight PST every day, and weekly leaderboards reset at Saturday midnight PST."
AFAIK it is not possible for you to reset your leaderboards manually, other than deleting /unpublishing them.