After the 5th treatment is done, how often you have to do the laser removal like once a year?

Usually hair removal treatments are the most effective after 6 in the initial phase. Then I recommend follow-up treatments at least yearly, if not every six months, to address newly formed follicles and growth. Your laser technician should be able to provide the best advice for your specific case. "This
answer has been solicited without seeing this patient and cannot be
held as true medical advice, but only opinion. Seek in-person treatment
with a trained medical professional for appropriate care."