Assuming it is Synchronous,
after selecting the slot feature from the PathFinder, click the word in the callout called "Slot 1" that appears on the slot feature in the graphics window.
I started my previous reply with posting some images, but it is so frustrating to see the images not appearing in this forum after several attempts. It simply refuses and does nothing.
I have updated the original reply with links to images.
Please check them.
Thank you very much Tushar, I have seen your images on the links, the problem is I have created the part with the slot in ordered not synchronous so the callout does not appear, how do I modify the slot radius in the ordered environment ?
In ordered, select the slot feature in the PathFinder and select the 'Edit Definition' from the floating bar.
Then from the Command Bar, select the first button 'Slot Options' to edit the width.
So this procedure is why I avoided using the slot tool and just sketch the slot out. When learning software stuff like this makes it frustrating.
I may start using the that feature in the future to easier hole/slot alignment