Hey Roberta,
great, thanks for the screenshots! I can see there by looking at the third screenshot, that NodePit is currently obviously not properly installed – otherwise it would show up here:
Could you again go to this step please: File → Install KNIME Extensions…
In the installation window, could you try to untick the following checkboxes:
- Show only the latest versions of available software
- Group items by category
- Hide items that are already installed
Then, just to try a different path, do not enter anything in the “type filter text” field, but instead scroll all the way down to “N” and see whether NodePit for KNIME appears in the list:
Keep me posted! 
Philipp