"Methods for increasing HRV include the following:
Intelligent Training. Don’t overdo it and push too hard for too many days without giving your body an opportunity to recover (see below).
Hydration. The better hydrated you are, the easier it is for your blood to circulate and deliver oxygen and nutrients to your body. Aiming to drink close to one ounce of water per pound of bodyweight each day is a good goal.
Avoid Alcohol. One night of drinking potentially decreases HRV for up to five days.
Steady Healthy Diet. Poor nutrition has adverse effects on HRV, as does eating at unexpected times.
Quality Sleep. It’s not just the amount of sleep you get that matters, but also the quality and consistency of your sleep. Going to bed and waking up at similar times each day is beneficial.
Auto-Regulation. In general, trying to get your body on a consistent schedule (in particular with sleep and eating to align your circadian rhythm) is helpful. Your body does things more efficiently when it knows what’s coming."
Learn More: 10 Ways to Improve Your HRV