How should I go about training my voice to sing like this?

Okay so first off I have no access to vocal lessons so pls don't suggest that lol ik that would be the best thing but that's basically impossible.
So I'm looking to sing Nightmare by Halsey not the first thing I would pick to sing bc I'm a contralto who doesn't have a natural ability to belt, but I was told to sing this song n yeah I have no choice. My voice is smooth, syrupy almost if you will, breathy at times, and intentional voice breaks are easy for me to pull off. But this song has a raspy rock edge to it. Check out the live lounge performance halsey did n listen to the chorus. How do I get tht raspy kind of shout? Every time I try my voice kinda goes into high n breathy mode or a middling sort of belt but just plain no rasp or shout to it. Is there any technique or exercise tht would help with this? I'd appreciate any help you could provide bc I need to have this song perfect in around a week. Cutting it close but yeah. Urgent help needed.
https://m.youtube.com/watch?v=HW_EmCGc6DI
This is the link to halsey's live lounge performance.