It is currently impossible to reset progress, in-game, on Adventure Mode without deleting the actual save files.

Xbox One and PS4 users are in this sketchy situation where Adventure Mode is locked until a requirement is met in Score Attack (in turn, must also be unlocked by the Tutorial). And no one wants that. Those platforms may be unreliable for runs until Bandai Namco provides a solution, unless you are willing to give an hour to unlock Adventure Mode for another go at Any% or 228.

EDIT: I have looked at the save file, and while you do have to redo the tutorial, you'll need D's in courses you need to unlock Adventure Mode. Theoretically, if you fail (lose all lives) with a D, you'll still unlock new courses and, eventually, Adventure. It could help slash recovery times even further.

Switch players have it easy on the other hand. Have a 2nd profile ready for runs. Adventure Mode is already unlocked for you, so just be cautious on which saves you're deleting (personal vs speedrun) before doing an attempt.

Regardless, for all consoles, have a separate save or profile for speedrunning, just in case. Not sure how it works on XB1 or PS4, but it's the only alternative I can think of if you want your scores intact. Back up your normal save as well, if you don't want your high scores lost.