One of the many definitions of fitness is the increased ability of the lungs to absorb oxygen in the air, into the bloodstream via the alveoli. A fit person can put a lot more oxygen per breath, into the bloodstream. This excess of oxygen often results in a lowered heart rate to compensate. If the effects of Covid - 19 are to attack the lungs ability to take up oxygen, it is fairly obvious that a fit person might be in a better position to deal with a reduction in lung oxygen uptake than the equivalent unfit person. If you are overweight or obese, that usually, but not always goes hand in hand with low cardiovascular fitness.
Therefore, Obesity will almost certainly effect the outcome of Covid- 19 in a negative way.