Go to Retail > Wholesale Location and click + Add new. The form is the same as a retail location (name, address, state, switches, hours, fulfilment days, Grab&Go days, cut-off) with these differences:

• Wholesale Menus - a multi-select of the wholesale menus this location is allowed to buy from. Without at least one menu the wholesaler has no dates or meals to order.
• Discount (%) - the percentage taken off your normal meal prices when this wholesaler orders stock.
• The fee field is labelled Cost to deliver instead of Pickup Fee.
• There is no stock-alert recipients section.

After saving, assign the location to the customer account(s) that run it: edit the user under Users and pick the location in Wholesale Settings > Select Wholesale Location. From then on those users see Wholesaler / My Wholesale on the customer site. Active wholesale locations are limited by Max Active Wholesale Locations on the Retail config tab.