Silicone is an artificial rubber that is much more resilient than natural rubbers. In order to melt silicone, it must be heated to over 316C. Depending on the age of the silicone, it may actually break at this point. Also, this temperature is a difficult and dangerous heat for most individuals to achieve with household appliances. Therefore, the easiest and safest alternative to shrink a silicone wristband is to cut it and reconnect it.
Wrap a piece of thread around your wrist as loosely as you would like the wristband to fit. Cut the thread at this point.
Wrap the piece of thread around the wristband to measure the amount that needs to be cut to fit your wrist.
Cut out the section of the wristband to where the thread does not extend.
Squeeze a thin bead of silicone glue on one inside piece of the cut surface of the wristband.
Pull the opposite cut ends of the wristband together to allow the silicone glue to reconnect the wristband to a circular shape.
Squeeze another thin bead of silicone adhesive on the inside of the wristband and place in a cool place to dry for 12 hours before wearing.
To extend the life of your wristband and the new silicone adhesive seam, don't wash and dry the wristband.
Close the silicone glue as soon as you are finished with it to avoid the tube drying out.