Though Oracle hasn’t provided straight forward method to disable TDE . But there is a work around for this.

Follow Below steps
Find the encrypted table columns and modify them:


Now find the table under encrypted table and move to normal tablespace:



switch logfiles multiple times

Close the wallet, move the wallet files and restart the database:



Now TDE has been disabled. Now if you want to enable TDE again, then restore the wallet files and open the key.