IRS Notice 2007-7 says the following:
Q–36. Is the exclusion for qualified charitable distributions available for distributions from any type of IRA?
A–36. Generally, the exclusion for qualified charitable distributions is available for distributions from any type of IRA (including a Roth IRA described in § 408A and a deemed IRA described in § 408(q)) that is neither an ongoing SEP IRA described in § 408(k) nor an ongoing SIMPLE IRA described in § 408(p). For this purpose, a SEP IRA or a SIMPLE IRA is treated as ongoing if it is maintained under an employer arrangement under which an employer contribution is made for the plan year ending with or within the IRA owner’s taxable year in which the charitable contributions would be made.
https://www.irs.gov/pub/irs-drop/n-07-07.pdf
If you made a SEP contribution for 2017, you cannot make a 2017 QCD from the SEP IRA. You would have to move some of the money from the SEP IRA to another IRA and make the QCD from the other IRA.
