A return is automatically locked after it has been e-filed and accepted. There are no setup items related to this option. You will see one of two messages depending on your security level for Drake Zero or Web1040.

If you are not an admin, you will only see the options Continue in read only mode or Back:

If you are an admin, you will have the options Unlock return, Continue without unlocking return, or Back:

All users have the option to View EF Detail for the return.

If you need to file an amended return, you will need to have an Admin user unlock the return.