To search for messages on the iPhone version of WhatsApp, open Chats and swipe down from the screen. Tap Search, then enter a search keyword and select the conversation you want from the search results.
Step
Method 1 of 2: iPhone

Step 1. Tap on the WhatsApp icon on the home screen of the phone

Step 2. Tap Chats

Step 3. Swipe down the screen to show the search bar

Step 4. Tap the search bar

Step 5. Enter the keywords you want to search
You can search for sent messages, or contacts you've chatted with. WhatsApp will search your entire conversation to display the results.

Step 6. Tap on a conversation from the search results to open it
A conversation will open, and the keywords you entered will be tagged.
Method 2 of 2: Android

Step 1. Tap on the WhatsApp icon from the list of phone apps

Step 2. Tap the Chats tab

Step 3. Tap the magnifying glass icon at the top of the screen

Step 4. Enter the keywords you want to search
You can search the contents of the conversation, or the contacts you have chatted with.

Step 5. Tap a conversation from the search results to open it
A conversation will open and the keywords you entered are marked.