Use your fingernails or a tool to pull inward and outward on the top inner corner of the fabric-lined plastic around the lens to pull it off it's plastic clips.

Do the same on the bottom inner edge.

Now the whole inner side should be loose and have a bit of play in it.

If you're too rough with it, the fabric can become dislodged from the plastic ring it's attached to. If this happens, you should be able to glue it back into place once it's out.