Kydex and hybrid leather/kydex holsters are built to a "happy medium" in terms of retention. Some people prefer almost no retention while others want their holster to be clamped in tight.
Increasing retention:
UNLOAD AND CLEAR your firearm, insert it into the holster and place the holster on a flat surface. Take a couple of towels and get them damp, not soaked. Place the towels around the holster so that only the trigger area is exposed. Heat up the kydex with a blow dryer. It will take a minute or two of sweeping the hot air across the kydex before it starts to soften, you will notice it area inside the trigger guard starting to raise up. At that point take a corner of the towel and press the kydex back down into the trigger guard (forward of the trigger,but behind the trigger guard) be careful not to push the kydex down so far that it would touch the trigger while holstering. You are trying to "pinch" the kydex around the forward part of the trigger guard. The area around the ejection port and the forward part of the trigger guard are where kydex holsters get their retention. With a little heat and pressure you can dial in your preferred level of retention. There are probably some YouTube videos that can explain this better than I can with some visuals. Also, if you see the kydex starting to get shiny you've got it too hot.
Edit: ALSO!! once your holster has cooled down, put on your holster and do some dry practice to make completely sure that the kydex in the trigger guard area won't depress your trigger while holstering. While unloaded and clear set your hammer or striker "cocked" and holster the weapon several times trying to mimic the different pitches and angles you could possible insert the firearm to insure that the kydex will never touch the trigger.