Hello,
First I invite you to have a look on this
documentation
to learn how to use the override system.
From what you describe previously, there are good chance that you make some custom code directly in view file.
That could explain why some custom code can be erased while an update, on the other hand the override view will always be kept.
Now, in order to achieved what you need follow me step by step :
1. Go to your Item Menu settings (Menus => Main Menu)
2. Click to edit the Item Menu
3. In Product options tab, reproduce this configuration red bordered elements.
4. Then process an override, for your button and his link you have to use the code that add the
dynamic url within the product image (to go to product page)
Hope this will help you to achieved what you need.
Regards