Go to Library, then select Agency Suppliers.

Switch to your personal agency if needed. At the top of the page, you'll see your host agency listed by default. If your suppliers were created under your personal agency, select your personal agency from the dropdown to switch views.

Click into the supplier you want to map.

Click "Edit Supplier" in the top right corner.

Search for the matching supplier in the host supplier list. Use the host supplier search field to find the same supplier from your host's library.

Click "Save & Close" in the top right corner. The supplier is now mapped to the host supplier.