Oleksandr, good afternoon
I think one of the easiest ways is to massively change the presence of the supplier in the list of products like this:
1) in the settings "Edit window" /app/product/masschange/block/ add the block "Supplier" and enable the checkbox "Add settings" Available from the supplier" yes
https://i.imgur.com/OsUGBKr.png2) filter the goods of the desired supplier
https://i.imgur.com/VOeOmVo.png3) mark all and change availability like
https://i.imgur.com/fZMtXBW.png and Save
4) if you have an automatic recalculation of availability configured in your system after changing data on suppliers, then the availability of the product itself must change instantly, unless, of course, there is no availability of the same product at another supplier.