In Model view, select the table whose properties you want to view or set. In the Properties pane, expand the Advanced section, and expand the Storage mode drop-down.
Changing the Storage mode of a table to Import is an irreversible operation. After this property is set, it can't later be changed to either DirectQuery or Dual.
You can know more here : https://learn.microsoft.com/en-us/power-bi/transform-model/desktop-storage-mode