Heyy Thank you so much for playing my game it means a lot ! Indeed this game needs a tutorial haha i'm actually working on it right now !
For the manual part, i wanted it in even though i could have put an automatic but if you want to try again the advice is to shift up when the sound stops getting higher (it actually starts doing a brpbrpbrp sound from the rev limiter) and to shift down in turns as you slow down.
I also have a few plans for such a starter lap (it would be in Feira de Santana probably)
This explanation will be in the tutorial eventually :p