OnePlus
Search a Conversation in Messages auf OnePlus
The Messages app on OnePlus phones only searches inside the conversation you have open, not across your whole inbox. That is why the search icon sits at the top of a single chat instead of the conversation list.
To use it, open Open the Messages app ➔ Choose a conversation ➔ Tap on Search. A search field appears where you can type any word or number that might be in the message.
After you Enter a keyword and Tap on Search again, the app highlights every match in yellow and jumps to the first result. Small arrow controls let you step forward and backward between all matches without retyping the keyword.
If nothing turns up, check the spelling first, since the search only matches exact text and ignores typos. It also will not find text inside images or MMS attachments, only the actual message body.
If you are trying to find a message from a contact you no longer see in the conversation list, this in-chat search will not help either, since the conversation itself needs to still exist and be open first.