The RR login credentials are stored under the RR_User table. (select * from RR_user but pw will be encrypted)
Please refer the ID and you can reset the password as required from SQL or run the below query to insert the new user(555) with blank password:
insert into RR_user( Number,Name,Privileges) values (555,'555',1)
Note: Please make sure you have the db backup before running any query.