How do I file a 1040 if I don't have one?

[xmasbaby0]

A 1040 is the tax return form you prepare here to send to the IRS.   If you start entering data in this software you are preparing a Form 1040.   Please look at it so you will know what you are sending to the IRS:

PREVIEW 1040

https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing

Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.

[VolvoGirl]

What income do you have?  Like W2 or 1099NEC or 1099Misc etc?  Are you asking how to enter your self employment income without a 1099NEC or 1099Misc form?

Just enter it as Other self employment income or as Cash or General income.  You don't need to get a 1099NEC or 1099K.  Even if you did you can enter all your income as Cash.  Only the total goes to schedule C.