Hi,
Thanks for get in touch with us.
Well, this is a very basic feature and works with all WC standard themes.
There has setting option for this as well – https://ibb.co/DrHFzTv
Check here in our demo site – http://wcfmmp.wcfmdemos.com/product/store-manager-download-documentations/
But, I think your theme is not a standard WC compatible theme and destroyed WC default hooks so this is not visible as per expectation.
Please be sure you didn’t disable “Sold By” option by mistake – https://ibb.co/Qft4PJ1
And please try Sold by Template Tab once – https://ibb.co/Qft4PJ1
Between, which theme you are using?
Well, one more thing – be sure you are not trying for vendor user created previously using some other multi-vendor plugin. If so, then change their user role to “Store Vendor”.
Thank You