how can i recover my viber chat

Hi

The developer's instructions for restoring Viber messages (but no other content on your iPhone) from a backup are detailed here:

Viber | Back up and restore Viber messages

If you make regular backups of your iPhone, then you may otherwise be able to recover the content by restoring your iPhone from a recent backup. Note that any new content since the date of the backup would be lost:

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

For any further assistance with using the Viber app, I suggest that you consult the app developer's other support resources and/or contact the app developer:

• Viber | Support Portal
• Viber | Open a Ticket

Viber is not an Apple product, best you check it with the app developer on their forum/website.