i have removed parts of it and wrapped it but not the entire grille but i suspect removing it will be the same way of removing that large plastic top cover under the bonnet and unclipping it from behind to pop it out.
i posted a downloadable pdf manual for the zb here which might help, just get the "Zipped PDF Manual" and have a look for something related to the grille replacement
this is a manual based on the 2018-2019 buick regal(ZB commodore). it is 9000+ pages of mess but can be very useful ;) Zipped PDF Manual EDIT: i will add these here too... MY18 Commodore Brochure PDF MY18 Commodore Owner Manual PDF Service and Warranty Booklet PDF
You'll have to remove the front bumper to get to it. The grille is probably held on with screws or plastic clips.
While you're at it, check the radiator for Galah guts clogging it up. The engine won't be able to cool itself down as efficiently if there's bits of a bird lodged in it.