Doogee S88 pro Malware + install custom rom

I purchased the Doogee s88 Pro a year ago, and it is the perfect phone for my rugged lifestyle, except of the uncertainty of them installing malware / adware in their devices.

I’m trying to install a custom ROM, just normal android with SP Flash Tool, but I can’t seem to get it to work. Is anyone able to give steps?

I have the following:,

AOSP,
ADB,
mtk drivers,
SP FLASH TOOL,
SCATTER FILE for device provided by manufacturer.

However whenever I try to direct the “boot” record in SP flash tool, I get a error saying “is this the correct one?” Which then I can’t proceed.