Single-leg or single arm exercises are known as unilateral exercises that should be performed on both sides.
For unilateral exercises, Fitbod will indicate how to properly log these. For instance, Dumbbell Lunge will display # of reps PER LEG and the amount of weight PER ARM (image below).
*Important Note: If you are using an Apple Watch, you won't see this configuration from the Fitbod watch app. This configuration will only display on the phone app.