I have undergone a penile frenectomy, but the skin under the frenulum is still tight. When erected, foreskin barely retracts over the glans. Options?

See your urologist. Minor surgical correction, the tight frenulum can be released with a simple surgical incision under local anaesthesia by your urologist.
Circumcision. If there is no reason not to have one, a circumcision would certainly help, and the frenum could be retreated at the same time. All depends on your goal of treatment. Good Luck.