Possible to upload all files of a said extension?

[Nazband]

Hello! First of all, i don't code so it took me forever to understand how it was working but i felt proud when i did! Now all i'd like to know is how i can make it so every .mkv files in my folder are scanned then uploaded to youtube. I tried various things like *mkv or *.mkv but yaml slap me with the "invalid argument." Would you know by any chances how i can incorporate that in your script?