You need to mail in the 8453 form with your 8949 form since that form was checked on your 8453 form.
Use Form 8453 to send any required paper forms or supporting documentation listed next to the check boxes on Form 8453
When and Where To File
If you are an ERO, you must mail Form 8453 to the IRS within 3 business days after receiving acknowledgement that the IRS has accepted the electronically filed tax return.
If you are filing your tax return using an online provider, mail Form 8453 to the IRS within 3 business days after you have received acknowledgement from your intermediate service provider and/or transmitter that the IRS has accepted your electronically filed tax return.
If you don’t receive an acknowledgement, you must contact your intermediate service provider and/or transmitter.
Mail Form 8453 to:
Internal Revenue Service
Attn: Shipping and Receiving, 0254
Receipt and Control Branch
Austin, TX 73344-0254
