Go to whatsapp – settings – chat settings – Backup conversations click on it, it will create a backup of your current conversations.
Step 3- Clear Whatsapp Data
Go to Phone settings – Applications – Whatsapp – Clear Data
Step 4- Go to File explorer /sdcard/whatsapp and rename the whatsapp folder to OGWhatsapp.
Step 5- Install OGWhatsapp (unofficial Whatsapp app).
Step 6- It will ask for phone number. Give the old number through which you have registered on old whatsapp.
OGWhatsapp is ready now.
Step 7- Install normal Whatsapp for another account.