Should I wait until I receive my paper check to amend? How am I supposed to do after I receive the paper check?

[Maya1]

I am a J1 visa holder, and I've filed my tax return for 2018 with Turbotax and got accepted (my paper check is on its way). 

However, I realized that J1 visa holders could not use Turbotax to file, and I would like to amend. I think I need to wait until I receive the paper check and mail a new form to IRS, but should I put the paper check that I receive from IRS in the envelope to send it back with the new form? 

Also, do I have to amend by April 15, 2019 ? 

Thank you 

[WillK]

You should not try to amend your return until the original return it has been fully processed and you have received your refund or your payment has cleared. Amended returns do not “catch up” to your original return and replace them; they are processed as two separate returns.  

Amended returns have to be printed and filed by mail.  It can take the IRS up to 12 weeks or longer to process them.   If you are due a larger refund than on your original return, your amended return should only show the difference and you will receive a separate check for it.  If you owe money on your amended return, it will show only the new amount owed, you will have to mail a check with the return. 

[Maya1]

Thank you for answering my question. I now understand that if I owe money then I need to mail a check with the return. I am just wondering how I am supposed to send back the refund that I have received as a result of the wrong form?  
Can I send the paper check that the IRS has sent to my address?  
Or should I make separate checks, the one is for the amount I have received from the IRS and the other one is for the amount I owe? and send them with the new return?   
Thank you