How to get value from custom input added to products

Hello people,

I have followed this link in order to add a custom field within the products entity, but, I couldn’t find a way to change its value. For instance, In this specific case the input is setted as manufacturerId, but, I would like to be able to use other value there and save it on my plugins table.

I also did the following docs named Database migrations and Adding complex data to existing entities (they are currently all there in the plugin) the only thing I’m missing is how to fetch data from an input that has a „differente name attribute“ or something like that.