Once you have downloaded the ZIP file on your PC, follow these steps:
1) Right click on the file, select 'Extract All' and follow the
instructions to unzip it.
2) Run the BlueStacksInstaller.exe file to install this Android emulator
on your PC.
3) Now, in BlueStacks, click on ‘Play Store’ and log in with your Google
account.
4) Go back to the BlueStacks home screen and drag the WhatsApp
Business.apk file over it, and you’re good to go.
If this doesn't work, go back into 'Play Store' and search for the app to
install it directly from Google Play.