From February 1: WhatsApp to shut down support for these phones

Several smartphone models may not be able to run WhatsApp from February 1, 2020

If you're still using OS versions mentioned above, here's what WhatsApp recommends following the shutdown https://faq.whatsapp.com/en/android/26000006/

On December 31, 2019, WhatsApp withdrew support for Windows phones. Now, WhatsApp will withdraw support for older versions of the most popular operating systems from February 1, 2020, according to the WhatsApp FAQ section.

However, the instant messaging app will keep its system running for select phones — with KaiOS 2.5.1+ OS, including JioPhone and JioPhone 2.

The older versions of Android (2.3.7) and iOS (8) operating systems "can no longer create new accounts, nor re-verify existing accounts after February 1, 2020."

If you're still using WhatsApp on these phones with lower version of OS — and don’t want to lose all your chats and information after 1 February, 2020 — there is an option to save your chats: [1] Open the chat you wish to export, and tap on Chats. [2] Tap ‘Export Chat’. You’ll then be given the option to download the chat with or without media. Choose your option and export all your chats.