* Automatic Transmission: Simply move the gear selector lever to the "N" position. This is usually located on the center console.
* Manual Transmission: There's no true "neutral" for the *drivetrain* in a manual transmission Blazer in the same way an automatic has. To achieve a neutral state for the wheels (meaning the engine isn't directly driving them), you need to depress the clutch pedal fully and put the gear selector lever into neutral (typically between 1st and reverse). The drivetrain is still engaged mechanically, but the transmission isn't transferring power to the wheels.
If you're having trouble shifting your automatic transmission into neutral, there might be a problem with the transmission itself. If this is the case, you should have it inspected by a mechanic.