5 year visa renewal (Ho Chi Minh City)

Hi everyone, I recently moved to Vietnam and obtained a 5 year visa exemption. Currently living in Phu Nhuan (near district 1). The 5 year visa exemption requires the foreign citizen to only continuously live in Vietnam for 90 days and then they would have to leave the country and return, OR go somewhere and pay $10 to get it renewed (every 90 days). I'm quite not sure where this can be done. For those who have done this, please let me know where I can get it renewed close to where I am. Thanks!