I'm a 23 year old man with a undescended testicle what procedure do i need to undergo to fix this problem?

Seek a consultation: You need to see a general surgeon or urologist. They must decide if your testis is somewhere in your groin, abdomen or was just lost. Since abdominal testis are more at risk of testicular cancer & can interfere with your fertility it would need to come out. Whether they could move it to proper position or not at your age is less important.They can give you a prosthesis if you want one.

Removal of testis: If you are a 23 year old male and have an undescended testis, it is unlikely to function. It may require removal. See a urologist and or general surgeon. A thorough exam, you most likely have just had and the testis was not found. The doctor will need to see if the testis exists. Talk with your doctor about how to proceed. There are artificial testis available that can be utilized.