In Teams, you can find and resume a previous conversation. No matter how many times you’ve spoken to that person, it’s all in one place.
How to find an old message
All your old messages are saved, and you can search for them (and people, chats, and files) using the command box at the top of your screen. Click the conversation you want to resume.
To search for an attachment, look in the Files tab above your search results. You can click Filter 
to narrow your results.