How to make directory/file writable?

To make a desired directory/file writable, simply change file permissions to 775, if you want everyone to be able to write into the directory, set the permissions to 777. It can be done via file manager from the cPanel or via FTP client. Right click on the file and select "Permissions".

Here is a tutorial on how to use File Manager on Hostinger shared hosting servers, you will see how to add change the permissions there too - https://www.hostinger.com/tutorials/how-to-use-hostinger-file-manager/