A.Your best option would be to right-click the database copy from the Exchange Management Console (EMC).Thereafter you should select Remove.
B.your best option would be to run clean-mailboxdatabase -identity -ex03 from the exchange management shell.
C.Your best option would be to right-click TKDAG from the Exchange Management Console (EMC).Then the Manage Database Availability Group Membership should be selected thereafter -ex01 should be removed from the list and manage clicked.
D.your best option would be to run remove-mailboxdatabase -identity -ex03\-ex01 from the exchange management shell.