Thanks for your reply @ErnieS0 . Your method worked for me to make a negative adjustment to my self-employment income on TurboTax Online so that I don't owe any self-employment tax. This ended up deleting the Schedule SE from my return, while keeping my Schedule C which is perfect. However it also deleted Form 1040 Schedule 2 from my return, I suppose because I don't happen to have any other "Additional Taxes" other than the self-employment tax which is now deleted. But I can just print out a blank Schedule 2 and write the "Exempt, see attached" note on Schedule 2, Part II, line 4 (Self-employment tax) and attach my exemption certificate.
Also, thanks to @Hooktrunk for your advice. I may have very well given up on TurboTax sooner had I not already paid for it this year and pretty much completed my return except for this one issue. When you use expatfile dot tax, can you eFile with the IRS and attach documents electronically so you don't have to mail in a paper return to the IRS? Turbotax won't let me make any attachments if I eFile. So I still will have to send the IRS my proof of enrollment in foreign social security every year I have self-employment income. Per SSA.gov guidance on social security totalization, "a self-employed person must attach a photocopy of the certificate (foreign social security coverage) to his or her income tax return each year as proof of the U.S. exemption."
