Give access to digital product when phisical item is brought

Hello,

I’m trying to sell an item with an associated video course. The video course will be available on the website, as soon as the customer has completed the purchase of the physical item.
It’s like an online guitar video course, associated with the purchase of a physical guitar.
But we don’t want to sell the digital course without the purchase of the physical item. We sell only this item in the shop (for the moment) so I would like to avoid premium plugins if possible.
How can I do this?