Zheng Ruotong (in English grammar, commas are used to distinguish surnames from first names)
Generally speaking, self-introduction is to say your first name "Ruotong" before your surname "Zheng":
If the first name is written before the last name, there is no comma.
If you want to choose another homophonic English name, you can consider: Toni, Tonya, Rona, Ronnie.