Stock Trading without Visa

I opened a Robinhood account for purchasing stock when I had non resident visa(J-1).

Now it was expired and I came back to my country, but I am still trading stock in Robinhood.

If I earned income in the stock market, do I need to file my tax return?

If so, how can I do it?

Can I file it by 1040NR?

 

I appreciate your answers.