Problema with cdvDebugSigningPropertiesFile is null

I work on Ionic, and I have an app in a customer who have distribute the app to all of sellers arround the country.

I made the app on my Mac and now, I sold my Mac and buy a PC. I built my app in debug mode, with the command ionic build android and I get a android-debug.apk file. Now, when I compile in my PC and deploy the apk in the android device who has a previos compilation with the Mac, I can’t install the new version because I have the message " An existing package by the same name with a conflicting signature is already installed ".

I saw that gradle is who sign the apk, ¿is correct? And in this case, ¿Wich sign use to this?