Soapy water also kills the good guys.
Give the plant a good rinse using the spray nozzle on your hosepipe or watering can to clean off any residue and then check daily for aphids and just squish with your fingers until you see the good guys coming back to eat them.
If you don't like, or can't do, regular squishing you can make a garlic spray to deter aphids without harming beneficial insects.