While I am
Not familiar with that model of camera, I have successfully cleaned several focus screens.
To clean the underside is easy, go in from the front with lens off and mirror down.
Usually to get to the upper side generally requires removal of the top cover and prism which is a piece of cake on some cameras but a right pain on others.

The cleaning method I use is a damp tissue folded up and held in fine tweezers. Careful not to touch focus screen or mirror with tweezers and only wipe gently and change the tissue a couple of times.
This will clean off dust but will not harm the screen.
Fresnel screens are generally made of a very soft plastic that is fairly vulnerable to chemicals, so I'd be cautious of using anything much stronger, although a water based lens cleaner might work.
Straight water works well enough for me so far.