How convert simple products to products with variables?

Hello,

I have csv file with simple products, but want to make variables – same product: t-shirt red, t-shirt blue, t-shirt black are same product in different lines with different IDs (like different product), has no SKU section, there are no identifier.

Tried to google and found that can do what I want with Sheet editor plugin – it is not free.

Do you know other free plugin or easy way how to make my problem solved (CSV file is big – more than 1000 lines).

P.S. Wish You understood my problem ??