If a database no longer exists, or if you want to disable connections to a specific database, then you can delete all login credentials for that database from the wallet.
To delete database login credentials from a wallet, enter the following command at the command line:
mkstore -wrl <wallet_location> -deleteCredential <db_alias>
wallet_location is the path to the directory where the wallet is located. The db_alias can be the TNS alias you use to specify the database in the tnsnames.