I found out from @num3ric where you can turn on the plugin(which is still in beta)
Plugins → Editor → Level Sequence
Editor (check Enabled)
[EDIT] Lol… I watched the video and it showed exactly how to enable the plugin… I apologize.
I completely misundertood your question and thought you were not able to find where to enable sequencer like I was… Again, sorry lol…
So… my answer was wrong. Converted to comment