So we did some digging and are bringing you the answer!
The way to reactivate used silica gel (out of the sachet) is:
USE THE OVEN: This method gives the best results even though it takes longer. Set the oven for 135C. Place the silica gel in an appropriate container and dry the gel until it turns medium blue. Take out, let cool and it is ready for use!
USE THE MICROWAVE: Place the silica gel in an appropriate container and set the microwave power to the medium to medium high setting. Dry for approximately 3 to 5 minutes and inspect the gel for color change. If the gel has not dried, stir it withy a spoon and heat it for another 3 to 5 minutes. Stir the gel each time it is inspected. The actual heating times will vary according to the type of microwave.