Back Drill

Design > Layer Stack Manager > Menu Back Drills

Select +Add > Properties Panel > Select First and Last Layer

Save Stackup to PCB

Design > NetClass > i.e. BackDrill > Add Nets

Design > Rules > High Speed > Max Via Stub Length

Select Net Class > BackDrill

Set Max Stub Length

Set Back Drill OverSize

Apply

Tools > Remove UnUsed Pad Shapes..

Repour Polygons and Review the Back Drills in 2D and 3D.

That's it !

Back Drilling Vias

Interesting Links . . .

Back drill vias - Altium Discussion Forums