The 49200's HEPA filter lasts an average of 2200 operating hours (if it is on continuously, this is approximately 91.67 days); this also depends on how many particles are in the air; if it is only turned on when the room is very dirty, the filter will fill up faster.
The replacement filter can be ordered through the following link:
https://www.trebsshop.com/en/products/49201-hepa-filter-smart-airpurifier