No, you cannot delete a message on Stroll. You can however, delete a conversation by unmatching with the person on the Matches screen.
To delete a conversation:
1. Tap onto your Matches Tab
2. Tap the conversation that you want to delete
3. Tap the three dots on the top right corner of the screen and select Unmatch
Unmatching is an irreversible action that will delete a conversation and remove the user from your Matches tab permanently.