Hi @eftcolumbus,
Thanks for reaching out to us.
At the moment, you can assign a product to one vendor only as seen in the image below.
I have raised this as a feature request with our development team to let the admin assign a product to multiple vendors. I’m not able to give an ETA if and when it can be implemented. We’ll keep you in the loop for updates.
In the meantime, I’d recommend duplicating the product in bulk via CSV and assigning it to each vendor in the “Vendor ID” field. Please check this documentation for more details: https://woocommerce.com/document/product-csv-importer-exporter/.
Thank you for your understanding. Feel free to contact us again if you have other questions.