To link Customer and Vendor on web, please follow the steps mentioned below.
Step 1: Click on Vendor.
now, for your desired customer you want to link with vendor click on them and select Edit option.
Step 2: Now click on +Link Customer.
Step 3: Search for customer and click on Link Customer and Update Vendor.
Note: By clicking on link customer we will fill the customer details and the customer will be linked to the vendor.