Unfortunately, there isn't an out of the box way to achieve this with how O365 has modified the context menu.  One of the alternative methods is to trigger it with a metadata change or start when a new item is created.

updated: @aizotov812 I completely misread this post. @JohnHernandez solution is correct in that you can reference it by typing the name of the workflow in. 

Hi!  

Yes.  You will need to enter the Workflow name you wish to start.

I will reach out to our product team to see if we can update this action to align with 2010, so that it give you and other users the ability to select available lists.  

I'll also share our help document on the Start a Workflow action using Nintex O365 if you haven't seen it already.

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