If your husband does not have a Social Security Number, I would recommend that he get an Individual Taxpayer Identification Number (ITIN). In order for a person to be able to file an income tax return or to be claimed as a dependent on another tax payer's tax return, the IRS requires that they have either a Social Security Number or an Individual Taxpayer Identification Number (ITIN). For your convenience I have included a link below where your spouse can apply for an ITIN so that you will be able to include them on your 2018 income tax return.
Individual Taxpayer Identification Number: https://www.irs.gov/individuals/individual-taxpayer-identification-number
Without your spouse's SS# or ITIN, you will not be able to efile a married filing jointly or married filing separately tax return. The only other option would be to paper file your return as married filing separately.
Please read this TurboTax FAQ for information on “How do I amend a 2017 return on TurboTax”:
How do I amend a 2017 return
in TurboTax?