I have created a request approval process, but instead of having it look up the manager in AD, i want users to be able to add the name of who they want the request to go to from a set field call managers name.
So not sure I really understand your request. You can do one of three things.
Option 1: Create a list of managers in SharePoint and connect your Manager field to that. (this is not ideal, but doable)
Option 2: Create a SharePoint group for the managers and in the people and group field, select the sharepoint group to restrict what people can select. This is the best route.
Option 3: Create the field as normal, but have it as a free form people picker where people can select from Active Directory.
Once you have that setup, create a workflow that takes value of that fields and uses that for the person to assign the request to. Should be good from there.
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