If you're a very longtime user of Pixlr apps, you may be acquainted with the Liquify option. It has always been available in Pixlr Express on the web. While a lot of features in Pixlr apps are available in multiple apps, Liquify isn't one of them. It's only available in Pixlr Express, so you won't find it in Pixlr for Mac or PC or Pixlr for iOS or Android.
However, you can also find similar and perhaps even more advanced options in Pixlr Editor, our online graphic design app. Pixlr Editor has tools that also allow you to "pinch" and "bloat" which is similar to how Liquify works.