What works for us is using a large flat blade screwdriver that we have ground the sides down to fit inside the charging handle slot of the upper receiver. Slide it into the receiver with the receiver upside down to lift up on the gas tube if needed. We also use it by inserting it from the top to pry the gas tube to the center. Remove the bolt from the carrier to check the gas tube/key fit by sliding the stripped bolt carrier into the receiver. If it’s the gas tube note which way it is deflected so that it can be adjusted until there is no resistance felt when the stripped bolt carrier is installed.