A research from WHO has revealed that “the virus” ( you know what i mean ) can only live on any surfaces for no more than 9 days. Actually, 9 days under perfect conditions is the max period of time “the virus” can survive.
So what you need to do is to place your mask in a plastic bag, put the date on the bag and just wait. You can overkill by placing the plastic bag under the sunlight.
I’m not recommended using microwave for sterilizing masks. I don’t have any data proving that microwave is good or bad for killing the virus.