I have two sets of Lambda Pros and one Sigma Pro, all with the following
semi-trivial problem: the nearly transparent plastic air filter-type
material that keeps human ear detritus away from the grids has
disintegrated.
The plastic "window screen" is intact, and the phones are fully functional.

I would like to do the repair myself.
Does anyone know how to remove the cushions, in order to gain access to this
foam material?

It looks like standard plastic air filter material will work here.