If you change password of Oracle USER1 wrongly

Go to the previous backup or copy of database and select user's password hash

SQL> SELECT name, password  FROM sys.user$ WHERE name='USER1';

NAME
--------------------------------------------------------------------------------
PASSWORD
--------------------------------------------------------------------------------
USER1
48F7196FF1A87215

On the problem DB change password by issue:

SQL> alter user USER1 identified by values '48F7196FF1A87215';

User altered.