KiCAD ver 5.1.4 to Altium AD19.0.8

Assuming you have KiCAD source files.

KiCAD > File > Fabrication Outputs > Drill

Precision 2,4

KiCAD > Plot Gerbers

Use Protel filename extensions.

Altium > New > CAM Doc (Camtastic)

File > Import > Drill. . .

Units. . .

Tool Table. . . 

Define Tool Table (Drill sizes)

Tables > Layers, set Top to Top and set Drill to Drill Int.
Tables > Layers Order > Set Physical Layers

File > Import > Gerber
Place > Flash
Tools > Netlist > Extract > Wait for it . . . 

File > Export to PCB

That's it !