A customer is meeting with an agile team at regular intervals and keeps changing priorities...

 In an agile environment, the product owner is the key stakeholder who represents the customer’s interests and has the authority to prioritize work for the team. If a customer is frequently changing priorities, it can disrupt the team’s workflow and progress. Therefore, the project manager should ask the customer to discuss these changes with the product owner. This way, the product owner can assess the impact of these changes on the project’s goals and the team’s workload, and then appropriately adjust the priorities. References: 

https://onlinepmcourses.com/impediments-obstacles-and-blockers-how-to-address-and-remove-them/

https://www.scrum.org/resources/blog/scrum-master-impediment-remover