Form 8606 failed to file for spouse

You have 2 options ... you can amend the return if needed and attach the 8606   OR   mail in the 8606 on it's own.  

Did your spouse either make a new non-deductible Traditional IRA contribution, take a Traditional IRA distribution (have a 1099-R) or do a conversion to a Roth IRA?   If not then there should NOT be a new 8606-S.

Also, if one of the above does apply then you might have not indicated that the contribution or 1099-R was for the spouse and it went on a 8606-T instead.