As is known to us all, we can use iTunes to back up our iPhone data. When we lose important data such as contacts, photos, videos, etc., we can reset our iPhone and then restore these data from iTunes by setting the iPhone up again. However, this may cause another problem - all the existing data on iPhone will be replaced by the previous backup we synced, which means we will lose the data created after the synced backup we choose. Then, is it possible for us to keep that part of data? Actually, it is possible as long as we extract WhatsApp messages from iPhone backup.

Then, how to extract the data we want? Look at this post and have a try:
Extract WhatsApp Messages from iPhone Backup


Hope it will be helpful for you!
You can extract WhatsApp messages from iPhone backup iTunes and iCloud directly, but it doesn't support us to do it selectively.
for detailed steps, you can refer to below article :
Methods about Recovering Lost WhatsApp Voice Message on iPhone

and when you want to extract WhatsApp messages from iPhone backup selectively and directly without erasing all content and settings, you can come to iRefone for help.
for detailed steps, see below article for reference:
Restore WhatsApp Messages on iPhone
iPhone Data Recovery for Mac will be a good choice for you to recover whatsApp messages from iPhone backup. It is designed for all iOS users to recover lost or deleted contacts, photos, messages, notes, videos, music, calendars, etc from iPhone/iPad/iPod, iTunes/iCloud backup files in 3 simple steps. First to choose data recovery mode, second to scan and preview data, third to recover lost data in seconds.