i want to join this jam, but i don't know how to upload scratch games to itch, can you guys please help me?

(sorry for bad eng)
You can convert it and export it using Turbowarp packager!(it's an website) 

(i'm pretty sure) the jam requires the game to be in html5 format

Ihope it helps :D

You can use Turbowarp:

https://packager.turbowarp.org/

Gandi IDE can help you and Here is a step-by-step guide for you.