PUMP_FAN1 is for the fans on the radiator I believe. From the looks of it though, the fan cables are built into the radiator/pump on this specific AIO, so you shouldn't have to worry about that.
The pump itself usually either goes in the AIO_PUMP header or the CPU_FAN header, but your mobo doesn't include the former and the manual recommends the CPU_FAN header anyways, as Lutfij said.
Which Rev. version of this AIO did you buy? While I was researching I noticed that Rev. 3 often comes with the wrong mounting screws for the AMD AM4 mount, double check that yours are correct. If not, fill out
this form and they'll ship you the correct screws for free.