How to Clasp a Traditional Wrap Bracelet
Determine which loop on the cord would be the best fit for the sizing of your wrist.
Then you can spread the loop open to be able to insert the button.
If the existing loops don't line up for the best possible fit for your wrist, you can untie the knots and move them so that you have the perfect fit. Just make sure to leave enough room between the knots for the button to fit easily.
Insert the button through the loop.
Once you confirm that the bracelet is sitting the way you want on your wrist you can trim off any excess cord that you don't want. Just make sure to leave approximately 1/2 inch past the knot so that it doesn't pull out.
For increased strength, you can add a drop of superglue to the knot and pull it tight before you trim the excess cord.