You should find the answer to your question in the Bitwarden Help section below.
Q: How do I “unshare” an item from my organization?
A: To unshare an item:
Clone the item back to your individual vault by navigating to your organization vault (by selecting Organizations from the menu bar, not by using organization Filters) and selecting Clone from the Options menu for the item you want to clone. Only users with user type admin or higher can clone items into their individual vault by changing the Ownership setting.
Delete the item from the organization vault by selecting Delete from the same menu.