I'd probably start with basic chemistry and organic chemistry, and cell biology, and probably physiology would help. Once you feel like you have a solid understanding of those, biochemistry, immunology and pharma will be accessible.

I'd start with YouTube and MOOCs. Unfortunately, I don't watch too many videos about this stuff, so I don't have any specific recommendations.

There is also the Manga series, which some people find more accessible as a narrative format: https://nostarch.com/biochem https://nostarch.com/mg_mbiology.htm https://nostarch.com/physiology

Also, keep in mind this field is rapidly moving forward. Crispr was discovered after I graduated, which wasn't that long ago. Try and stick to newer materials where possible.