How to Set a Flag with Shell "If" Condition [Duplicate]

I am new to shell and I have never actually worked in it. I have a build script and i want to export a flag to "true" or "false" based on the condition in the if statement. My code is

echo "Is the Build with GAPPS?(arm64 only)"
set_gapps_build=false
select yn in "Yes" "No"; do
case $yn in   
        Yes ) set_gapps_build=true;
        break;;
        No ) set_gapps_build=false;
        break;;
    esac
done
if [ "$set_gapps_build" = true ] ; then
        export SAKURA_GAPPS=true
        export TARGET_GAPPS_ARCH=arm64
fi

If i choose true, the flag should be set to true but its not working. It remains to false. Incase you want to see the whole shell code its here..