Albert. Most striker fired pistols, particularly Glocks, cannot be de-cocked. To release tension, you'll have to remove the magazine, check the chamber to ensure it is empty and pull the trigger full cycle to release the firing pin. Finally, there are no external safeties on a striker fired pistol.

James G some striker fired guns have a manual external safety IE Ruger SR series

It keeps the striker (firing pin) from hitting the primer unless the trigger is pulled. When you pull the trigger the trigger bar moves the striker safety leaver up depressing the striker safety. Once the striker safety is depressed it is out of the way of the striker and the striker can move forward all the way and striker the primer.