Calling a sub from a different userform

Hi All,

I'm having trouble with a userform calling subs.

In Userform1:

Private sub CommandSubmit_Click()
SubmitForm.Show
End Sub
This shows userform2 which lets the user confirm submission or cancel to go back. When the submit button is clicked:

Private Sub CommandSubmit_Click()
Call SubmitDataTrue_Change
End Sub
This calls a sub from the code of userform1, but if I test and click submit, I get an error "compile error sub or function not defined"

I hope this is enough info. Thanks for the help in advance!