Changing the portfolio items slug prefix
Generally the portfolio item URL will look like this: yourdomain.com/portfolio-item/the-name-of-your-item. But you can change the "portfolio-item" prefix. Learn how in this article.
You can change the slug prefix for your portfolio items by going to Theme Options » Portfolio tab. Write the slug you want inside the “Portfolio Items Slug Prefix” input.
Important: You must flush your permalinks after you modify this option.
And you will probably need to refresh the Portfolio Transients (Theme Options » Portfolio tab » “Refresh Portfolio Transients”). If you don’t see your changes being applied, start with that.