You can edit or delete your messages after sending them so that they disappear for you or for everyone.
iOS: To edit or delete messages, go to Chats → open any chat → long press on a message → choose an action (Copy, Forward, Reply, Edit, Delete, Share via… or More. If you want to select multiple messages → select More → select as many messages as you want and Delete or → select Delete All.
Android: To do so go to Chats → open any chat → tap on a message → choose an action (Copy, Forward, Reply, Edit, Delete, Share via… If you want to select multiple messages → long press → select as many messages as you want → Delete them.
Delete for Me/ Delete for Everyone
Delete for Me deletes your selected messages from your side (your phone). You can choose to Delete for Me to delete any message (yours or a recipient’s) anytime you want.
Delete for Everyone deletes messages from your phone and the recipient’s phone or group’s phones. You can only select Delete for Everyone for messages that you sent in the chat yourself, within 3 days of sending them.