Thread a needle with about 18 inches of thread and tie the ends together
Position the button where the original button was or where it should be attached
Push the needle from the back of the fabric to the front through one buttonhole
Pull the thread through until the knot is secure on the inside
Push the needle down through the opposite buttonhole and back through the fabric
Repeat several times through both holes to secure the button
If the button has four holes, sew in an X or parallel pattern
Wrap the thread around the stitches under the button a few times to create a shank if needed
Push the needle to the inside of the pants and make a few small stitches to lock the thread
Tie a knot on the inside and trim the excess thread
Check that the button is firmly attached and moves properly if needed