Talk to Pediatrician on Undecended Testies

I need the advise on it...my baby boy was born in the seconds day of his 9 month...and now he is four months old .. at the time of circumcision I have noticing that he has undecended testies..right side not in his scortum while left side testies are ok... pls advise me what's the best time for surgery or it will be automatically takes its actual place etc someone pls share the contact of an experience piadratic sergen.