Make iPhone that was reported lost unlost?

I have a iPhone 5S that I got on T-Mobile and I had recently reported it lost since I thought I left it in a Pizza Hut. But, I later found that it was at home. I need to unreport it lost so I can use it again.

Have you tried just calling the place where you bought it and explain what happened

Call your carrier, you may not be able to because it might be permanently blacklisted once reported.

Contact T-Mobile about it. Or whoever you reported lost to (likely T-Mobile anyway)