I purchased a car but the seller had 07 on the title because he was going to sell the car at the time but the buyer never bought it. What can I do about changing the date, or what can I do?

Depends on the state you live in. Check with the DMV. In some states a notarized letter will suffice. Make sure the VIN is correct and matches on all parts.

The date on the contract between you and the seller showing the date you bought the car should be correct (you do have a contract, right?). Also on the title the seller could cross out the original incorrect date and write in the correct date of sale, and initial the change.