There is no possibility to delete a supplier entirely if it already keeps some history logs in the system. But you can disable a supplier, so it won't be available and visible in Precoro.
To disable a supplier, please follow these steps:
1. Please go to the Supplier Management → tab and click on Manage Suppliers;
2. Click on Show filters and find the supplier that you want to disable;
3. Then in the Action column, click on the edit button;
4. Move switcher in the right side of the 'Edit Supplier' row to disable the enabled supplier or vice versa (a switcher should be grey and show "OFF") → Update.
Now your supplier is disabled.
You can always enable it again, just check this article.