pour oil on troubled waters
US /pɔr ɔɪl ɑn ˈtrʌb.əld ˈwɑ.tərz/
UK /pɔr ɔɪl ɑn ˈtrʌb.əld ˈwɑ.tərz/

1.
to try to make people feel calmer and more friendly toward each other when there is a disagreement
:
•
She always tries to pour oil on troubled waters during family arguments.
•
The manager stepped in to pour oil on troubled waters after the heated debate.