Get the vamp or toe piece, fold it in half, then find the midpoint, and mark.

Sew it around with a 3/8 seam allowance, then leave a 4 gap, and trim the excess.

3 Sizes DIY Fabric Slippers Sewing Tutorial

3 Sizes DIY Fabric Slippers Sewing Tutorial

Image credit: made by JOJO via YouTube

Easy DIY Fabric Slippers Sewing Tutorial

How To Sew DIY Fabric Slippers