Go to the BP_GridComponent and copy the video below. Note make sure you copy the Default Value of the PresetGridSizes variable before deleting it like shown in the video.

When you try to delete the PresetGridSizes variable (This is not the variable you create in the video, this is the variable that was already in the component) the engine may crash due to an engine bug in newer engine versions.

If this happens go back to the BP_GridComponent and change the PresetGridSizes to a Boolean variable type and Save the blueprint. When you compile the engine will crash, but reopen the project go back to the BP_GridComponent and now you should be able to delete the PresetGridSizes variable.