How to add QT_QPA_PLATFORMTHEME=qt5ct environment variable in Arch Linux?

I am using a standalone tiling window manager QTile. In QTile I want to organize my GTK and QT Themes. For GTK theme I used a program named "lzappearance" and it works perfectly fine. But, for Qt I am using a program named as "qt5ct". On the top it is written this application is not configured correctly and when I click on the information button it says: The QT_QPA_PLATFORMTHEME environment variable is not set(required value: qt5ct). Please help and guide me on how to set qt5ct and environment variables.