According to a post by WABetaInfo, WhatsApp might soon let iOS users search for messages on a particular date. The feature is currently available on WhatsApp beta for iOS 126.96.36.199 update from TestFlight.
It looks like WhatsApp has added a new calendar icon which might show up when you are trying to search for a particular message in a conversation. Clicking on the button opens up a calendar view where users will be able to pick a date. If you want to dismiss the calendar view, just scroll through the conversation and it will disappear.
The newly added feature will really come in handy if you want to look at when you first talked to someone or if you want to read messages sent on a particular date.
Keep in mind that you will have to sign up for the beta if you want to use the latest WhatsApp features. It is interesting to note that developers were reportedly working on the same feature two years ago but seemingly discarded the idea at the time.