This has been discussed here, https://www.speedrun.com/tts/thread/223em But to reiterate: after beating a level, press the "repeat" button, and while the screen fades out, press the "next level" button. Keep in mind this will interfere with your best times for each level.

I got it. But why the PB is 15.80 in level 1?

That PB may have been set when it was possible to move before the level fully started. This was patched early on. Another explanation is that a time from a later level was applied to L1 since beating L40 puts you back at L1.

Oh I understood thank you

that was from when i found you could die to complete a level i think, not sure (i've forgot a lot about the game, me sorry)

@Ayden this one is other glitch, you can play the level again and it counts as a new level. To do it you have to press restart and right when the next level screen is starting to appear and press next level, or something like that