To enter Liverpool Street station from the north you need to be driving a train ;-)
From Appold Street/Pindar Street, walk along Primrose Street and turn right onto Bishopsgate. That will take you to the concourse entrance next to Hamilton Hall (which is rather grandiose Wetherspoon's pub at Liverpool Street). It's quicker that way than heading for the other end of the concourse (and if you're catching a Norwich train it will also take you closer to the platform that it leaves from).