The form requires this to be a manual entry. It is sufficient to write something to the effect of, "I received 1099-MISC after filing. Please find a copy attached to this form." Or, "I incorrectly entered 100 instead of 200 on my previous W-2 entry." Just be honest and clear about why you needed to send your state amendment form.
Also
include any documents relating to the changes you made, for example any W-2s or
1099-s that weren't included on the original return.
If you need any additional guidance, please comment back.