Try stretching it. Use your fingers to gently spread the opening OR get an erection and pull down on the shaft skin. Don't force it back, it can get stuck. Just move it as far as you are comfortable. The more often you do this the sooner it will stretch.
There may be some discomfort. Doing it in the shower may help under the warm water.
You'll likely find your glans very sensitive. This is normal.
Your doctor/urologist may prescribe a steroid cream to help the skin grow.