Pivot points are in beta at this moment, if I am correct you are unable to use them for anything like this.
If you do want to rotate a part around a certain point use the following:
local PivotCFrame = CFrame.new(PivotOffset)
Part.CFrame = Part.CFrame * CFrame.new(PivotOffset) * CFrame.Angle(0, math.rad(i), 0) / CFrame.new(PivotOffset)