How to fix squeaking in carpeted stair treads
The squeaky floor repair kits have a special rod that you "drill" into the floor. If it slides up and down easy, you missed....move over and try again. Once you find the stringer, use the special screw, driver bit, knock off/standoff and drive the screw in. Break the head off and walk on,the step to see if it's fixed. After fixing the first step,  the next step will be easy to fix.