You shouldn’t do your brakes with that question

Grind it off with a random driveway rock. Beers

Did it come like that? Can you not take it back to wherever you purchased from and ask for a different rotor or a refund?

Razor blade. Scrape it off, it’ll be fine.

Brake clean

It’ll be gone in the first brake application.

Did you try break clean

Lick it off. You don’t want to break a nail scratching it.

Looks like extra casting material. You can either sand that down with an orbital and 90 grit - or let your pads get rid of it the first time you step on the brakes.

Scotch Brite or steel wool. They make both in a scale of abrasiveness. It’s what they recommend to scuff rotors.

The brakes will kleen it

I would try with slick new scraper/spreader/spatula for wall works width 2 inch or so then by positioning it on rotor against residue at as small angle as possible.

like this one https://www.amazon.com/dp/B09FL49JP5/ref=sspa_mw_detail_0?psc=1&pf_rd_p=07d4f2af-6342-4249-a50e-928411266fe1&pf_rd_r=CWWWFPP2E94DZF1D4F8A&pd_rd_wg=JnjFs&pd_rd_w=zoscX&content-id=amzn1.sym.07d4f2af-6342-4249-a50e-928411266fe1&pd_rd_r=8810baac-ed38-4402-bc52-ab3d943ac8e9&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9kZXRhaWxfdGhlbWF0aWM&th=1

Spray them down with brake clean wipe them with clean towel, good to go.

If brake cleaner doesn’t do it and scrapping it isn’t effective. You could get them turned. Or do a return

Shop teacher taught us to always hit a new rotor with some sandpaper to knock off the glaze. Do that and you’ll be good to go!