If your red dot sits lower than your irons you will need a riser rail for it to sit on. You will also need to consider if you want absolute or 1/3rd co witness when choosing which riser you will need.
Use your google-fu to search both absolute and 1/3rd co witness sighting options, then do your measurements and choose accordingly.
Here is some bedtime reading to get you started.
Absolute or lower 1/3 Co-witness | The Professional Gunfighter