Related products

I have a dilemma, I made a block of related products, to be able to put in each product, I did the test with this product:

https://siraconcrete.com/producto/aurora/

Now I don’t remember how I did it to add this block only to the Aurora product.
Could you help me?
I can’t find how I did it…
And in the rest of the products this block is not there… I don’t understand