I would guess that the two main things would to make sure that any lingering pathogen was successfully treated, and then to steadily work to rehabilitate the lungs and blood.
If there is some lingering level of COVID, supplemental zinc and a zinc ionophore, like the prescription hydroxychloroquine, or non-prescription plant polyphenols such as the flavonoids quercetin (QCT) and epigallocatechin-gallate (EGCG – green tea extract), might help to resolve it. A liter or two of tonic water (they have sugar free varieties) has about the quinine activity of a dose of Hydroychloroquine. Maybe a course of antibiotics (like Azithromycin) to clear the decks of opportunistic bacterial component, like a walking pneumonia.
Stretching out the torso/shoulders/ribs and doing deep breathing exercises (like Yogic pranayama, or Wim Hof Method) to increase lung capacity, and doing cardio exercise, might stimulate improvements over time. Even if there is scarring, things will get some degree better with regular exercise, and likely some degree worse without it - so may as well make it a goal of your general exercise plan, to specifically increase the vital capacity of the lungs.
I saw some thing that I can’t reference, which theorized that another mechanism of COVID damage had to do with sugar damage (glycation) in the blood cells, so that a ketogenic diet might be useful during infection. That would hold out good hope for restoring function lost due to that mechanism, as blood cells are replaced over the course of months.
Regardless of the cause, get on a program to build general vigor and lung capacity - it is good no matter what.
Work that breath all the way in, and all the way out. Stretch! Stretch! Stretch! Max it out.