Any vendors you want to use should first be created in your connected Lightspeed Retail account and then imported (synced) into the app. Within the app, there are additional vendor details you'll want to fill out, but basic vendor details should be managed in Retail.
To import new vendors or sync vendor changes from Retail, go to Settings>>Vendors and click the "Sync" button. The app will then begin importing vendor data from your Retail account. Once imported, your vendors will show in a list on this page.
From your active vendors list in Settings>>Vendors, find the vendor record you'd like to update and click the edit icon button in that vendor's row. Here you can update:
For more information on these fields and how they work in the app, see the chapter under Manage Your Settings>>Vendors.