Hi William thanks for the post! I recommend using Actions and Layers to accomplish this - a layer on top of the main page that has the current process map can contain the sub-process you'd like to show and you can associate an action with a "+" shape to trigger that layer to open and close. I've demonstrated the steps for this below:

Starting with your original flow add a "+" text box (or shape/icon/text) of your choosing to the part of the process that you'd like to expand on. In the example below I've added the text "expand sub-process".

Next create an additional layer by clicking the Layers button in the bottom right corner then + Layer. In the example below I've named my new layer "Sub-process 1."

Next click on your new layer to open it and then build the sub-process within it. Note in the example below that I know my sub-process shapes are built within my new layer by the banner at the top of the editor that says Page > Sub-process 1 and because content on the main page is grayed out.

Finally create an Action to open and close this new layer. Select the shape or text you created that you'd like click on to reveal the sub-process then select the Actions button in the upper left corner of the editor. Within the Actions menu select the Layers tab and then within the Toggle dropdown choose your new layer. 

Now clicking that object/text will reveal and hide the layer containing the sub-processes when clicked! I've demonstrated this in the GIF below:

I hope this helps! Let me know if you have additional questions. 

Thank you for your response. This my current draft. 

So the challenge I am having is that I would like to add Sub-steps for each box. I used a template from Lucidchart trying to see if you have any suggestions on a template that I can include multiple sub-steps or how to expand on the current one. 

Hi Will in this case I would recommend either building out the sub process as a side-panel box adjacent to the main diagram - I've mocked up a general example of this using another template below:

Thank you so much! Exactly what I was looking for.

Is there a way for you to show me how you did that? I am more of a visual learner.

Happy to! First I added my text to the shape I wanted to click to expand the corresponding sub-process:

Next I expanded my canvas to create extra space to put this sub-process. I did this below but you can do this to either side above etc. 

Then I created a layer for the sub-process by clicking the Layers button in the bottom right corner then + Layer. In the example below I've named my new layer "Sub-process." To build within the layer simply click on it within the Layers menu. 

Next in the new space on your canvas (within the layer) build out your sub process.

Finally select the text you want to click on to open the sub-process layer then select the Actions button in the upper left corner of the editor. Within the Actions menu select the Layers tab and then within the Toggle dropdown choose your new layer. 

Then you'll be able to click and toggle the sub-process like in my example above! As a side note you can build multiple sub-processes in the same space on the canvas - you don't need to expand your canvas to accommodate them all without overlapping. I've demonstrated this below - I've created an additional sub-process following the same steps and placed it in the same location as the original but distinguished it with a different color. I can toggle it in the same way (then revealed both of them at the end via the Layers menu so you can easily see how they're in the same place). I hope this helps!