It appears in that case keep your f8997 handy and just wait until IRS asks for the missing form.
Whatever you do, do NOT try to send in a paper return (after e-file).
I tried this last year by sending in a cover letter with the 1040 plus the missing form after an e-file. It really confused the IRS (it looked like I sent in two returns in their system) and it got very messy requiring several phone calls to fix it all - just don't. If you already e-file then let it process.
Here's the info on when to file an amended return which pretty much the only option you have after you've filed a return.
Math errors and missing schedules don't usually require an amended return:
Taxpayers usually do not need to file an amended return to fix a math error or if they forgot to attach a form or schedule. The IRS will correct the math error while processing the tax return and notify the taxpayer by mail. The agency will send a letter requesting any missing forms or schedules.
Source:
https://www.irs.gov/newsroom/mistakes-happen-heres-when-to-file-an-amended-return
