First choose your duct tape!
Tear off a strip and set it sticky side up on a solid surface
Tear off a second strip and place it on top of the first one. Sticky side to sticky side
Trim up the edges if needed
Take a strip about 1cm wide...
...and fold down the top of it...
Then stick it to the end of the bracelet; and that would be used as the fastener.
BUT, of course you can always just use some velcro
And fasten it like that :)
The creator of this guide has not included tools