You may cutting down carefully on the red arrow color (between white dot) about 2 cm.
And then try to wear. If your head can not go through , you may cutting more for 1 cm. until your head can through to.
After that you may find a little cloth to wrap at the edge of the cloth that you cutting and sewing many time to prevent the edge unravel.
Use the same color thread and cloth or difference if you like and you may sewing buttons on clothes if you feel loose.
Hopefully that will go well