Once all your thread tails are cut, you can insert the coincell battery into its holder and flip the small power switch. Your sequins should light up! If they don't, switch it off and check your circuit for shorts and loose stitching and try again.
Enjoy your new bow tie! A two-sequin circuit should last 22 hours on a single battery, and a four-sequin circuit should last about 11 hours.
Remove the battery from your circuit if you get caught in the rain!