Login error on installation

Hello,
i am installing my card to my online server but it showing me login errors. how can i solve this errors. errors showing below:
Error showing when i go with Root Username and password:
Warning: mysqli::__construct(): (HY000/1045): Access denied for user 'root'@'localhost' (using password: YES) in /home2/smarttec/clickshop.com.pk/system/library/db/mysqli.php on line 7Warning: DB\MySQLi::__construct(): Couldn't fetch mysqli in /home2/smarttec/clickshop.com.pk/system/library/db/mysqli.php on line 10Warning: DB\MySQLi::__construct(): Couldn't fetch mysqli in /home2/smarttec/clickshop.com.pk/system/library/db/mysqli.php on line 10Notice: Undefined variable: mysql in /home2/smarttec/clickshop.com.pk/install/controller/install/step_3.php on line 280Notice: Trying to get property 'connect_error' of non-object in /home2/smarttec/clickshop.com.pk/install/controller/install/step_3.php on line 280

Error Showing when i got with my owned created username and password in DB.
Warning: mysqli::__construct(): (HY000/1044): Access denied for user 'smarttec_mubeen'@'localhost' to database 'smarttec_CSS' in /home2/smarttec/clickshop.com.pk/system/library/db/mysqli.php on line 7Warning: DB\MySQLi::__construct(): Couldn't fetch mysqli in /home2/smarttec/clickshop.com.pk/system/library/db/mysqli.php on line 10Warning: DB\MySQLi::__construct(): Couldn't fetch mysqli in /home2/smarttec/clickshop.com.pk/system/library/db/mysqli.php on line 10Notice: Undefined variable: mysql in /home2/smarttec/clickshop.com.pk/install/controller/install/step_3.php on line 280Notice: Trying to get property 'connect_error' of non-object in /home2/smarttec/clickshop.com.pk/install/controller/install/step_3.php on line 280

Undefined variable: mysql in

You seem to use an older Version OC, not yet able to handle PHP-7.
Check this v.1.5.6.5 controller file, to find out, where to change mysql commands to mysqli
Ernie

i downloaded step.php file. tell me the location where i copy it