Is this outdoors? Edema is a cosmetic issue, but it may be indicative of small sucking insects or mites, humidity (with heat), lack of light, lack of ventilation, etc.

If it's indoors, I'd say, just add a fan or something. When I gave my indoor plants potassium sulfate, it reduced the edema (but it still happened without cooling the temperature). I didn't venture to use a fan, but I think it would have been a better choice.

Edema damage will remain where it already is, but new foliage does not have to be affected (if you fix the conditions, it should be fine).

I don't have experience with edema outdoors (I live in a semi-arid climate with plenty of ventilation—ahem, I mean wind).