You can generate this sort of statements using dynamic SQL, e.g.
select 'alter user ' || username || ' account unlock' as cmd
where account_status = 'LOCKED';
Following up on your latest comment, if you want to manually enumerate the usernames you can use a PL/SQL collection such as a nested table, e.g.
SQL> set serveroutput on
2 type users_t is table of dba_users.username%type;
3 my_users users_t := users_t('USER1', 'USER2', 'USER3');
5 for i in my_users.first .. my_users.last loop
6 dbms_output.put_line('alter user ' || my_users(i) || ' account unlock');
7 end loop;
alter user USER1 account unlock
alter user USER2 account unlock
alter user USER3 account unlock
PL/SQL procedure successfully completed.
To actually run the commands instead of just printing them, substitute