Unclip the ONT and the battery backup from the plastic housing, there's a couple of screws behind them.
Make sure you cover up the fibre connector well (tape a bag over it or something but try and avoid touching the end as you could scratch it), store the ONT out of the room that's getting dusty.
If you wanted to extend the fibre out of the room temporarily so you still have internet while the plastering is getting done then you need a singlemode SC APC patch cable and an SC APC coupler. The APC part is important and should get you a green connector. If you use a UPC connector you'll damage the end face of the fibre.