You can not delete individual messages on Slide. However, you can remove entire conversations by unmatching someone.
If you want to unmatch someone, please follow the steps below.
1. Go to the 'Message' tab, select the chat room of the person who you'd like to unmatch.
2. Click the options icon at the top right corner of the screen.
3. Press 'Delete this match' and confirm.
When you delete the match, you will disappear from their match list, the other user won't be able to message you anymore and any messages you've exchanged with them will disappear too.
Please remember that unmatching with another user is a permanent action and that once you have deleted the match, you cannot recover it.