First, add a ct-nice-scroll CSS class to any of your elements. You can do it using Classify plugin: put { addClass: "ct-nice-scroll" } into ID Attribute of your element (refer to this topic for more details: https://forum.bubble.io/t/classify-a-tiny-plugin-that-brings-css-power-to-bubble/67741).

And then, put a "Nice scroll: Init all" action to your client workflow, which fits best for the moment when the default scroll should be replaced (e.g. when all target elements are visible).

You can also have different scroll groups initialized by adding a suffix to your ct-nice-scroll-group-1 class and using the Group option on the Nice scroll: Init all action (e.g. "-group-1" suffix in this example).

Demo editor: https://bubble.io/page?type=page&name=nice-scroll&id=connectish-plugins&tab=tabs-1