Added a SSD on my 2019 Imac and now Bootcamp won't start

[herblaka]

Hey everyone. I just bought a 2019 Imac (MHK23BZ/A Intel Core I3 8GB 256GB SSD Retina 4K 21,5) and I asked my friend, who's a former Apple employee to install a 500 SSD drive (Western Digital Blue) and more RAM. I'm not in the US so Apple charges 4x what he charged me, anyway...

Now Bootcamp assistant won't allow me to install Windows. I had tried bootcamp assistant before I added the SSD and it worked fine. Is there a way I could work around that? If not, is there a tutorial to Install Windows on a partition on this SSD?

I'm on Catalina 10.15.7

Thanks.

PS: The guy who did this for me is busy and I am desperate.