The approach that the business analyst should take to begin this process is to schedule a meeting with stakeholders and create a journey map. A journey map is a tool that creates a visual representation of the steps or stages that a user goes through when interacting with a system or solution. A journey map helps to understand and document the user's experience, needs, goals, pain points, emotions, and touchpoints across their entire lifecycle. A journey map also helps to identify any gaps or opportunities for improvement or innovation in the user journey. The business analyst should schedule a meeting with stakeholders and create a journey map by asking questions, collecting feedback, drawing diagrams, and validating information.
Scheduling a meeting with stakeholders and creating a journey map helps to begin this process by engaging and involving them in defining and designing the new client onboarding process. References:
https://trailhead.salesforce.com/content/learn/modules/salesforce-business-analyst-certification-prep/customer-di