dying shapes onto a shirt

[easilyBaffled]

I want to get started in cosplay and my first step is this t-shirt design. I assume( and please educate me if I am wrong) that taking a shirt and dying it would be the best method. I know there are shirt dying tutorials out there, but what I am having trouble finding is a way to maintain the specific shapes the white circle in particular. I am looking for any and all advice how to do this thanks.
I intend to use a 100% cotton shirt if that helps at all.

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