I have a flat tire. What should I do?

My parents bought me a new Honda Civic last year and it already has 7,000 miles as of today. Yesterday, I took my sister to a party and then Walmart and that's it. Later that day, someone told me that my front right tire is flat. I went to check and it was flat. I told my dad and he told me to take it to Walmart tomorrow and get it fixed. He said to tell them not to replace the tire since this one is already new. He thinks that there's probably a needle or something sharpe in the tire. How do I tell the people at Walmart to not change the tire but just take whatever that caused the flat tire out? Also is it safe to drive with one flat tire? Walmart is like 5 miles away from my house. Thanks!

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