I'm sorry but this feature is not currently available. However, if you would like to add/change the suppliers in bulk for your products, you can use our premium add-on ATUM Export Pro. With this add-on you can export almost any kind of data of your site, in this case products, import it on a spreadsheet and modify it and then import it again to your site. On the spreadsheet, you can introduce the supplier for all your products in a fast way.
I leave you here the link to the documentation of ATUM Export Pro, where you will find useful info about how it works: https://forum.stockmanagementlabs.com/t/atum-export-pro-documentation
And the link to the demo site in case you want to try the free trial: https://stockmanagementlabs.com/addons/atum-export-pro/
Hope this helps,