Problem: Sunburn (Hosta)
Hostas are shade plants and cannot tolerate too much direct sun. Sunlight breaks down chlorophyll, the green pigment in plant leaves. Hostas cannot replace the chlorophyll as fast as it is destroyed, and bleach to a cream or white color. If the leaf remains in direct sunlight, the bleached areas then burn from overheating and die, turning tan or brown. They can tolerate more morning sun than afternoon sun, and tolerate more sun in cool weather than in hot weather.
You cannot repair the damaged leaves. Remove them if they are unsightly. To avoid further damage, move the hostas to a more protected location, or create some shade for them.