I tried out the Big Chunk category on January 16th, getting a 1:44,something time and I submitted it to the mods the next day. But then right afterwards, I tried the same category again just for fun and got around 1:25 and I wanna submit that one instead of the 1:44 one. What do I do?

just do a new submission, both will (hopefully) be verified but only the 1:25 will show on the leaderboard (unless you filter in obsolete runs)

You can also delete runs that you've submitted if you really don't want it there