Yhyjyk

What's called a person who works as someone who puts products on shelves in stores (for example in supermarkets)? For example, if one of theproducts is missed, then he adds it again. I was told (by non native English speaker) that "merchadiser" works here, but some dictionariesb (Cambridge, Colin) say that merchadiser is someone who sells products. So I doubt it.

In a lot of companies in the US, this job is called "stock associate."

The responsibilities can include receiving shipments, stocking items in warehouses or on sales-floors, and assisting customers.

Other possible terms are "store clerk" and "salesclerk."

In my state (MA) in the US, they call it a "stock boy".

In the UK I have heard and seen shelf-stacker or sometimes shelf filler to describe this role.

Cambridge Dictionary

Collins Dictionary

Dictionary.com

To add on to the other answers (stock clerk, stocker, stock associate, store clerk, sales clerk, etc.):

In some libraries, this job is literally called a shelver (although "re-shelver" might be more accurate).

Stock clerk is a term I have often heard and seen. It's widely used in job descriptions and job search sites, though Stock Associate has become more popular in recent years.

I used to do this as a job in Australia, our official title was 'Fill Associate' (as we filled the shelves) and we were more colloquially referred to as 'Fillers' or just 'Fill'

I would say stock boy or stock person. (There seems to be regional variation in this, I am in the North-east U.S. if that helps.)

shelf-stacker would be term used in the UK, Australia and New Zealand. A merchandiser works for the manufacturer or supplier of a product and visits stores to set up the shelves and/or in-store displays.