How do I put a .csv file back so it can be read by Google Merchant Center

Site URL: https://www.artistwebsites.ca

I've exported a .csv file of my products, and want to upload that file onto my site for use by Google Merchant Center. It will save me copying data into their interface.

Can anyone tell me how to do this?

It's a good thing I manually entered some products because it is definitely a challenge to get everything right! I've deleted several that came out wrong, and am waiting for my first product to be completely approved.