Retractile v Undecen
If the testicle is "retractile" then it can be easily manipulated into the bottom of the scrotum and will stay there a moment or two.
This does not require intervention. If the testis cannot be placed into the scrotum on exam by a medical professional, this is an "undecended testis" and may need intervention - surgery. It won't resolve after two yrs by itself.