If you no longer longer order from a supplier you can change their status to "Unavailable".
From the left hand menu select "Suppliers"
Identify the supplier you want to disable
Click the three dots
Select "Unavailable"
This supplier will no longer be available within the ordering flow.
Please ensure if a supplier is being removed , that you update all recipes which use products from this supplier to the new supplier's products, to ensure your COGs/costings remains accurate.