Hello sss64,
Thank you for reaching out to Apple Support Communities.
These steps may help:
"Shapes 
Click a shape, then drag it where you want. To resize the shape, use the blue handles. If it has green handles, use them to alter the shape.
You can highlight and zoom shapes using these tools:
- Highlight
: Drag the highlight where you want. To resize it, use the blue handles. - Loupe
: Drag the loupe to the area you want to magnify. To increase or decrease the magnification, drag the green handle; drag the blue handle to change the loupe size.
See Rotate and modify shapes added to a PDF for more options."
More details can be found here: Annotate an image in Preview on Mac
Hopefully this helps.
Cheers!