Hey there, another user of RocketDock! It's great, isn't it?
Here's what you do. First, make sure all of you new icons are extracted to a sigle folder.
Now, right-click on one of the icons in the dock and click Icon Settings
In the window that opens, click the Change Folder
button. Then, select the folder that has your new icons in it. Then press OK. That folder will now be added to the Folders
list of the Icon Settings
window. Select it from the list to see the new icons in the Icons