Going into new job to sign paperwork, but already have a 2 week vacation planned 3 weeks from now....

Took an offer on a full-time job as a receptionist. I'm going in tomorrow to sign paperwork and receive my training schedule (which is supposed to take 2 weeks). Should I tell them tomorrow that I already had a 2 week international trip planned, and what are ways I can work around this? I'm scared that they'll fire me on the spot, especially since the job is one with high turnover and they can hire someone just as easily as they fire someone. What is the best away to go about this?

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