Not all the Viber messages will be restored since Viber does't back up the hidden chat message history, media messages, etc.You can only restore your messages to the same platform (iOS to iOS, Android to Android) with the same phone number.

Make sure the Viber messages you deleted are contained in your last backup as the new backup will overwrite the previous one.

Your Viber account must have been connected to your iCloud account before you could back up your messages (Settings > iCloud > iCloud Drive > turn on ' Viber').

After that, all your Viber messages in the backup will be restored to your iPhone, including the deleted ones.

Reinstall Viber on your device and link it to the same phone number. Note that it requires you to connect your iPhone to a stable WiFi network. If you've backed up the deleted iPhone Viber messages with Viber message backup function, follow these steps to get them back. Restore Deleted Viber Messages from Viber Backup The following are the 3 options to restore deleted Viber messages from backup in different situations. In case you have backed up the deleted Viber messages before, then you can directly restore them from backup.

Restore Deleted iPhone Viber Messages from Backup

Doesn't Work on: Android 1.0 (API level 1) / Android 1.1 (API level 2) / Android 1.5 Cupcake (API level 3) / Android 1.6 Donut (API level 4) / Android 2.0 Eclair (API level 5) / Android 2.0.1 Eclair (API level 6) / Android 2.1 Eclair (API level 7) / Android 2.2–2.2.Part 2.

Android 2.3–2.3.2 Gingerbread (API level 9) / Android 2.3.3–2.3.7 Gingerbread (API level 10) / Android 3.0 Honeycomb (API level 11) / Android 3.1 Honeycomb (API level 12) / Android 3.2–3.2.6 Honeycomb (API level 13) / Android 4.0–4.0.2 Ice Cream Sandwich (API level 14) / Android 4.0.3–4.0.4 Ice Cream Sandwich (API level 15) / Android 4.1–4.1.2 Jelly Bean (API level 16) / Android 4.2–4.2.2 Jelly Bean (API level 17) / Android 4.3–4.3.1 Jelly Bean (API level 18) / Android 4.4–4.4.4 KitKat (API level 19) / Android 4.4W–4.4W.2 KitKat, with wearable extensions (API level 20) / Android 5.0–5.0.2 Lollipop (API level 21) / Android 5.1–5.1.1 Lollipop (API level 22) / Android 6.0+ Marshmallow (API level 23)

Viber for android 2.1 download