According to the PMBOK Guide, the project manager is responsible for managing the project team, which includes developing, leading, motivating, and supporting the team members. One of the tools and techniques for managing the project team is interpersonal and team skills, which include mentoring and coaching.
Mentoring and coaching are ways of providing guidance, feedback, and support to the team members to help them improve their performance, skills, and motivation. By providing routine mentoring and coaching, the project manager can identify any issues that may be affecting the team members' performance, such as stress, burnout, conflict, or lack of recognition, and address them accordingly. This can help maintain the project team's performance level and prevent further deterioration. References: PMBOK Guide, 6th edition, pages
349-350, 360-361; PMP Sample Test Questions, question 2.