2007 Mazda B2300 tailgate dent

There isn't one, at least not a good one. Check for a franchise called "Dent Craft" or something similar. The new car dealers in your area will know of someone. They make the rounds once per week to remove dents from trade-in cars. They use special lights and long metal rods to go through drain and access holes to massage the dents out and blend in touch up paint. Used to cost about $50.00 per dent in the '90s.

Auto body repairs are not a DIY job unless you are simply replacing parts. That is a talent that takes years of practice to hone.