How do you set a primary part to be able to rotate a model by script

this error comes up when i try rotate a model: “Model:GetPrimaryPartCFrame() failed because no PrimaryPart has been set, or the PrimaryPart no longer exists. Please set Model.PrimaryPart before using this” - how do i set primary partt? need an example

In explorer, click on the model then go to the properties.
Click this area:

then, again in explorer, click the part you want to set as the primary part