Update Field Item with Lookup Field?

I'm pretty sure this is really simple... but I can't figure it out.

I have List A with the Title column. When I create a new item in List A, my workflow creates a subfolder in Library B and updates the Name of the Folder with [ListA:Title]. However, I also have a Title lookup column in Library B. How do I get the workflow to write to the Lookup column in Library B?

I'm in O365 and I've been trying various actions like O365 Update Item:

It doesn't seem like I can write to the Lookup column upon initial action "Create List Item"

Cheers!