Schematicless PCB Design

Hi, new to KiCAD here but long time PCB designer using Express PCB software…

I need to design a 6 layer PCB without schematic entry. 3 power layers and 3 signal.
The design is already completed and tested and boards made, but the EPCB service uses non-tented vias which is unacceptable for BGA placement.

I’ve figured out most everything except how to I assign power vias to their respective layer manually?