Split-ForEach is designed to iterate over the elements of an itemized list - so, unless you're creating an embedded page for each manager, it's not going to really work.

There are a couple of options, depending on the actual requirement.

1. You could use a split-join shape, with an assignment for each manager, then use the ANY condition to return to the parent flow whenever one manager approves their assignment. The issue with this approach is the need to explicitly identify the number of approvals; if you need 6 in some cases, but 3 in others, that will make things difficult.
2. Create a common work group for the managers that can perform approvals, and then add one assignment for approval to the flow, routed to the work group. All managers will have access to the assignment, but after the first manager completes the assignment, the task is no longer available to any of the other manager and the flow advances.