You could try some light stretching or mobility exercises. Or look up 10-15 minutes workouts like yoga, low impact cardio, or even just do some warm up moves.
Breath in, focus on one body part, hold and make your muscles tight there. Breath out and relax muscles in same time. Super simple, can do anywhere anytime and helps to build the habit
If you are not able to do the exercise then just stretch out your body for 5 minutes. It will help to release all the tension in muscles.
One thing I like to do on low energy days is find a morning or bedtime yoga routine for beginners, they’re usually just light to moderate stretching that help me feel more energized in the morning or relaxed at night and as you become stronger or more flexible over time you can move on to more intermediate practices that will help you recover and strengthen you body and it’s mobility
Stretch, stretch, stretch. Even the greatest athletes need to stretch. The best thing about it is you can do it whenever, even when your tired. And who knows, maybe the stretch might give you that boost of energy to whatever exercise you had planned