You can also bring a reaction emoji by double-tapping on the message, after this, you can select and react from the emojis given here. Double tapping will show emoji inside the pop-up window here. If you want, you can take back the reactions ie Undo. By doing this, that reaction will be removed from you and the person who sent the message. One thing to keep in mind is that if you use Reaction Emoji on the message of your DM then the notification will be given to the sender.