I hope you will be securing these Edit user pages with Authorize attribute and other security.
But to answer your question, create a FindUser page and have a set of controls which lets the editor select a user to edit.
Then when the user to be edited is identified (e.g. in a grid, or search result) send a view model from the FindUser page to the Edit action as a string
e.g.
[Authorize(Roles = "Admin")]
[HttpGet]
public Action FindUser()
{
UsersContext = new ApplicationDbContext();
var userNames = UsersContext.Users.Select(x=>x.Name).ToList();
return View(userNames);
}
FindUser view
@model List<string>
foreach(var userName in model)
{
<a href="@Url.Action(" edit=", new { username = userName })">@userName</a>
}
</string>