1. Visit an affected house lot
2. Dismiss the message(s) (it is worth noting that you will need to act quickly here, as the messages will stack up if left unattended)
3. Enter the Home Store
4. Select the Automatic Pool Cleaner and either Send it to the Inventory, or Sell it
5. Exit the Home Store
6. Select an Adult or Senior Sim (also important, as younger ages cannot clean the pool), tap on the Pool, and select Clean Pool
7. Once the pool has been cleaned, you can place the Automatic Pool Cleaner back in the pool and it should work as normal once again.