Older version android - google play

Hello,

I have a build of traccar manager deployed on google play since 2021 now I got this error msg trying to download the app from an new phone mobile with recent android version 5.1
https://ibb.co/GFRQCZ0

Please what parameter should i modify in android studio before rebuild the app ?
is it targetSdkVersion ? If so what change i have to perform exactly.

Thanks

Why not upgrade to the latest official code?

Because i think there are no notable changes except colors and icons.
I have some customizations in my build and i want to fix this incompatibility issue very quickly without havint to run new project with recent code source.