Hi @numismy I was stuck for a while on this too but thanks to your thread I figured it out. I hope you have too but I thought I’d write it down for anyone else wanting an answer
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Create a text field that is what you want your slug to be. You can also dynamically create the slug using existing fields, and it will automatically change the text to lower case and add ‘-’ instead of a space. If there are multiple of the same text in your database, it will also automatically add ‘-1’ or ‘-2’ etc to the end of your slug to ensure all are unique.
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Go to Setting → API and ensure these boxes are ticket, as well as the data type you would like to work on
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Go to Backend Workflows and create a new API Workflow. Name it, and then set up a key, the type should be the type of data you want to set the slug for
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Add an action ‘set a thing’s slug’, which is under the ‘Data (things)’ tab. Set the ‘thing to change’ as the option available under “WORKFLOW DATA SOURCES”. This is the key that you set up in step 3 and is the info the API passes to this workflow. Then set up the slug how you want; if you want to combine multiple text fields to create a unique slug, I recommend using the dynamic input option ‘arbitrary text’ so you can set out a long slug using multiple fields. As I said before it will automatically change the text to lower case and add ‘-’ instead of a space.
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Return to your data. If you would like to run this workflow on only certain things, and not the whole data set, click ‘New View’ and then set up your conditions.
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Click ‘bulk’.
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Select your API workflow from the drop-down and click ‘run workflow’.
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Refresh your data to see your new slugs! 
I hope this helped; I, for one, always appreciate it when someone in the forum gives a comprehensive guide.