Just spin easy or do another recovery activity. Light yoga, easy jog/walk/hike/swim/ski. Or take off
Warm up for 15 min in low endurance zone. Then do the remainder of the ride keeping HR in the endurance zone. If your hr drops below your endurance zone on downhills that is ok the goal for this ride is just not to go too hard with your hr out of your endurance zone for more than 1 min continuously. This will help build the infrastructure ( muscle capillaries, mitochondria, blood flow) that will allow you to do harder efforts and recover faster. Remember you have to go slow to go fast. Cool down 10 min.