[pour] oil on troubled waters

to calm a tense situation with gentle or diplomatic action

She tried to pour oil on troubled waters by mediating between the arguing friends.
His speech poured oil on troubled waters after the scandal broke.
The manager poured oil on troubled waters by acknowledging the team's concerns.
Diplomats often pour oil on troubled waters to prevent escalation.
A kind word can sometimes pour oil on troubled waters more effectively than a long explanation.