The hole in the centre of the screen cassette is for the fixation of the screen: the set screw (for the top brackets) is located in this hole. The other holes (in the corner of the cassette) exist for drainage. You should not plug these.
The only part of the screens that get “plugs” are where the screws are recessed.
If you're missing these plugs, please contact our customer service team at customerservice@pergolux.au or you can submit a claims form.