I've removed filter and successfully put 3rd party filter.
I met the same issue. My Mavic Air original filter had a 1/2 crack on it and it affected photo results.
After struggling to remove original filter for a hour. I accidentally broke the filter and it helped to remove it.
First, by gently and carefully push the center of the crack with sharp object such as small driver.
The filter will be easily break. You make the hole larger and larger then you will remove whole filter away.
Then put 3rd party filter on the outer rim.