In most cases, there's no direct way to get into a course with Chem as a prereq. without having done Chem first unfortunately.
You usually have three major options:
1. Take a bridging course with Monash College. Usually programs like these will let you take the desired course after successful completion. Best to ask about these directly, although I did find
this link which may help.
2. Getting into a similar course that doesn't need Chem as a prereq. and attempt an internal transfer (e.g. if you want to study Biomed --> start in Science --> get competitive enough uni grades and try to successfully transfer into Biomed after a semester or two. If the course that you are hoping to get into has a lot of chemistry involved, I would recommend taking first year uni Chem, typically CHM1011 and/or CHM1022, to help.).
3. Taking the same course at another institute that doesn't need Chem as a prereq. and later try an external transfer (e.g. if you want Biomed at Monash, try first at Deakin --> get competitive enough grades and try to transfer into Biomed at Monash). When you start uni, ask about credit transfers to avoid any issues later down the line.