==>goto whatsapp (which you are using currently) and take backup of your chats
==>Uninstall whatsapp
==>Now use any filemanager like Esexplorer , X-plore etc and goto sdcard and find whatsapp folder over there
==>After finding rename it from
==>Now install WhatsAppCA which you downloaded
==>Open and put the number which you was previously using in whatsapp and taken backup
==>After verification and installation done, you can install orignal