F1 international student, filled forms in TurboTax, and get refund. However I was told I should have filled Form 1040NR, not Form 1040. How can I return the money to IRS?

I am F1 international student, non-residents.

I filled tax forms in TurboTax, and get refund now. 

However I was told that I should have filled Form 1040NR-EZ, not Form 1040. 

I have filled Form 1040X and 1040NR-EZ to amend it, yet how can I return the money to IRS?

After you file

If you are not receiving a refund by filing the 1040NR, you will need to send payment in the amount of your refund with your 1040X. 

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After you file

How to fill 1040X, if I would like to send the payment along with the form.