your condition is termed as unilateral undescended testis
. Normally both the testis develop in the retroperitoneum ( within abdomen) in fetal life and descend to their usual position in scrotum
by birth. Undescended testis usually descend in first year of life after birth depending on their site after which spontanoeous descent is unlikely.
The undescended testis is prone for some complications like infection, trauma, torsion and malignancy. however you need not be bothered much about malignancy as it is rarer than other complications.
you need to see a urologist
who will do a surgery to bring down your testis to scrotum depending on the location of the testis and your age.