talk (someone) down

Translations
успокаивать (кого-то)
The negotiator was able to talk the suspect down from the ledge.
Переговорщик смог успокоить подозреваемого и уговорить его сойти с карниза.
Definitions
To persuade someone to calm down or to reduce their anger, excitement, or anxiety; or to convince someone to accept a lower price or less extreme position during a negotiation.