A distribution that is sent to directly charity from a 401(k) is not a QCD. It can only be reported on Schedule A as a charitable deduction. As TurboTaxMichaelL1 said, to make a QCD using money that is in a 401(k) you must first roll that money over from the 401(k) to a traditional IRA and then make the QCD from the IRA. QCDs are only permitted from IRAs, not from qualified retirement plans like 401(k)s.
The problem is that the first money distributed from your 401(k) during the year is your RMD for the 401(k) and an RMD is not eligible for rollover. So if you want your RMDs to go to charity as QCDs, you'll have to roll over all of your 401(k) balance to an IRA (after satisfying the current year's RMD for the 401(k) since that portion is not eligible for rollover), and then you can make QCDs from the IRA.
