Boiling and steaming are both recommended by Dr. Peter Tsai, one of the people who developed the N95 masks.

Sadly his university replaced his original article with a link to a new website they've set up, but I found an article quoting it: https://www.msn.com/en-za/health/medical/how-to-clean-and-reuse-an-n95-mask/ar-BB12pavj