After selecting to add a new anonymization task the according settings dialog will automatically open up. By default a couple of settings are already configured, for example the randomization of IP addresses. This default setting is designed to provide reasonable sanitization without having to configure anything, at the price of all IP addresses being replaced by random addresses.
The section tree list on the left lists all layers or parts of a frame that you can anonymize or sanitize. When a specific section is set to do something it will be printed in bold letters so that it is easy to see which parts of a frame are going to be affected - or at least where the setting for the section isn't set to "Passthrough".
The "Tools" Button
If you want to start with a clean slate you can use the "Clear" option from the tool button menu, e.g when you only need to replace a few things and want to keep all the rest intact. The "Restore Factory Default" option replaces the currently set of options with the sanitization options TraceWrangler uses as a default when installed for the first time. You can set your own default set of options by selecting "Set as Default Profile", which can be helpful if you often sanitize capture files from a specific network and want to keep the replacements consistent.