There are two tips you could do at home to fix that problem. One of them is to wash the glasses with soapy water, according to AARP.
The Annals of the Royal College of Surgeons of England suggested in a 2011 article to wash the glasses with soapy water and allow them to air dry before wearing them with a face mask to prevent fogging.
“Washing the spectacles with soapy water leaves behind a thin surfactant film that reduces this surface tension and causes the water molecules to spread out evenly into a transparent layer,” the article reads. “This ‘surfactant effect’ is widely utilized to prevent misting of surfaces in many everyday situations.”
The fogging occurs when the exhaled air travels upwards and comes in contact with the lenses.
“The misting occurs from the warm water vapor content condensing on the cooler surface of the lens, and forming tiny droplets that scatter the light and reduce the ability of the lens to transmit contrast,” it said. “The droplets form because of the inherent surface tension between the water molecules.”
The second tip is to place a piece of folded up tissue paper between the mask and the mouth. This way, the tissue paper will absorb the moist air, preventing it from reaching the glasses.
Another hack the AARP article noted is to loosen up the bottom of the mask while keeping the upper part tight to allow the warm exhaled air to travel downwards instead. You can find glasses that fit your face at sites like https://www.eyeglasses.com/brands/ray-ban-glasses.