This question is the same as Move GNOME file dialog buttons. However,the answer given there didn't work for me. The answer was
gsettings set org.gnome.settings-daemon.plugins.xsettings overrides "{'Gtk/DialogsUseHeader':<0>}"
Typing the above, gave me the following error.
GLib-GIO-Message: 11:59:17.132: Using the 'memory' GSettings backend. Your settings will not be saved or shared with other applications.
Kindly, help me in solving this. I have also tried issuing the above command in sudo mode but without success.