I need help with declining a job offer and wonder what to say.

I just graduated highschool and was looking for a job so I applied to cds (sample handler at costco) which is owned by costco but a separate entity inside of costco. I've done everything required and I'm technically hired, but haven't been scheduled or been into orientation. Recently I heard back from a different job that wants to interview. If I get the job at the other place what should I do with the other job to decline it?

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