I want to enabled some php extension but those extension are not available please help me.
PHP iconv extension
They are installed by default.
you can install it if you know what php version is currently installed and running with what packages like on epel packages(which i am actually used to work) i can install anything for specific php version by just some simple commands like this one sudo yum install php72-common php72-gd if you want to list your php packages you can use yum list installed *php* hope it helps.
sudo yum install php72-common php72-gd
yum list installed *php*