Login to old website
League Manager is part of the old website, so you need to logon on there to access it.
See http://www.yorkshireha.org.uk/knowledge-base/uncategorized/logon-to-old-website/
Select League manager plugin
From the list of plugins, select 
to take you to the main League Manager page:
The main League Manager admin pages are list on the right and documented elsewhere in this Knowledge Base.