More a psychological tip - see it as a challenge to see how LOW you can keep your heart rate.
Can you pedal slowly enough to keep it below 85%? Great, then tomorrow see if you can keep it below 83. Gamify it.
Other tip is, breathe through your nose. If you have to breathe through your mouth, go easier. I’ve done 4-hour rides using this to control my power.
Oh, and instead of seeing someone overtake you and thinking “I need to catch him!” think “If this was a race, he wouldn’t even see my back wheel”.