You can insert a section break at the end of your text on
page 3 (Insert>Break>Next Pabe) and then apply numbering
to section 2 only or you can use a conditional IF Field.
For the IF Field method, Type IF PAGE > 3PAGE
Select the first PAGE and Press CTRL+F9, select the second
PAGE and Press CTRL+F9. Select the entire string and
press CTRL+F. Now right click and press Update Field.