Dry wiping tends to smear oils and grind in dust.
First get loose particles off with gentle puffs of air and then lightly wipe with a clean lint free material slightly moistened with a touch of clean water and working from the center outward with minimal pressure.
Finish with a dry pass and let it sit for a minute to dry.
Check for fogging.
If it went from cold to warm or humid, leave it uncapped in a dry room so haze can evaporate.
I had this happen after a damp shoot and it looked hopeless then an hour later it cleared up.
Test again in good light at a middle aperture such as f5.6 to f8 with a quick shutter and a high contrast target.
If the corners smear or the whole frame has a veiled look even after a careful clean and acclimation, you may be dealing with internal haze or misalignment and a service visit is the answer.
