How to ask for vacation leave as casual crew who hasnt started working yet

Greetings!

I got my first job at Maccas and completed the orientation 3 weeks ago. Disappointingly I have not been added to the roaster and it is almost a month since I got the job! I asked the manager and he said my training shifts will start "soon". As of typing this I don't have any shifts till the 12th of Nov.

Now here is the problem, I am an international student in Aussie, I will be travelling back to my home country for the summer holidays (2 months) on the 26 of Nov. I did mention this in the interview and they simply said ok (tbh I thought I'd lose the job because of this).

I'm disappointed if at all I'll be only able to work max 1.5 Weeks before I ask for leave and worried that will be a bad impression. At this point I regret declining other job offers! Any suggestion would be greatly appreciated.