Suppliers in Trakkit are specific to each machine. You can have the same product in different machines supplied by different suppliers.
To change a supplier for a product you have to change it at the machine level.
You cannot change a supplier for a product that already has a reorder for that product
How to change a supplier.
Go to Inventory / Inventory
Search for the product you wish to change the supplier on.
Click Edit
Change the suppler in the pop up box.
Click Save