You can try navigating to ://whatsapp.com on your device. However, the stock iOS 7 Safari browser lacks modern web rendering standards. You may need to download a legacy version of Puffin Browser or Opera Mini via the App Store's "Purchased" tab to load the web interface.
Android running OS 5.0 and newer* iPhone running iOS 15.1 and newer. WhatsApp Help Center whatsapp ipa for ios 712
Even if you install the app, you may face a "Please Update" screen or activation failure. You can try navigating to ://whatsapp