How to reset the stats displayed in the statistics tracker?
Solution 1:
From the wiki:
Statistics are stored in […]
world name/stats/<uuid>.jsonon servers.
https://minecraft.gamepedia.com/Statistics#Storage (archive)
<uuid> here stands for the UUID of the player, which can be retrieved for example with /data get entity <player_name>. Deleting the file will reset the statistics for that player. Deleting the entire folder deletes all statistics.
(Warning, not tested: Deleting the contents of that folder and then removing write access to it might make statistics never save. But it might also simply crash the game.)