You drive off any water it has absorbed and make it ready to absorb more, 200 degrees centigrade for 30 minutes would do, or you can do it longer at a lower temperature. https://en.wikipedia.org/? read more
Silica gel is a pourous form of sand silicon dioxide, you could heat it way above 300C without damaging it. read more
Silica gel can adsorb about 40 percent of its weight in moisture and can take the relative humidity in a closed container down to about 40 percent. Once the gel is saturated, you can get rid of the moisture and reuse silica gel by heating it above 300 degrees Fahrenheit (150 degrees Celsius). read more