First, may I ask why you would want to do this? Wouldn't it just be easier to put the button on the form you were using? Anyways, I will try to help.
You could try something like this. On Form2 add the Following Sub:
Public Sub Command2_Click()
'Your Code Here
End Sub
Now on Form1 we need to create this Public Sub:
Public Sub Command1_click()
Form2.Command2_Click()
End Sub
Now on Form1's button we need to add the following code:
Command1_Click()
This will make the button on Form1 access the code on Form2. Also you can add the following code to the button on Form2 so that button will carry out the same code as the sub:
Command2_Click() This isn't exactly what you asked for but this is close. If not, then this will get you started.