Ah ok, I recreated this. I have thge cylinder here, and I have selected my Add tool, and switched it to Add Cone.

I place my cursor over the face where I want the cone to snap.

If you click and drag, it will scale non-uniformly from a corner point…

but if you hold down Alt, it will scale from the center

If you hold down Alt and Shift, it will scale from the center AND scale uniformly

Click to commit the area of the base, and then move your mouse outwards to give the cone height


Hope this helps?