Teams uses something called ‘persistent’ chat. This means that items are saved in succession over an indefinite period of time. This can make important items difficult to find or refer back to in your history.
What you can do is to ‘save’ items so that you can easily refer back to them later.
To do this for a ‘Chat’ item for example select the message that you want to save, click the ellipsis icon and then click Save this message
When you need to review or find this item at a later date navigate to your profile icon and choose Saved
This will bring up a listing of all of your saved items