All you have to do is rekindle your connection, immerse yourself back into him again.
Simply mediate upon his sigil offer it blood, open the sigil and perform any exercise to connect with him.
You can simply recite his enn, or invoke him, what I love doing to get a very strong connection is reciting both incantations to summon the light and dark aspects of Lucifer, then afterwards recite the Litany Of Lucifer.