I am unable to find "new tab" after adding Site Aggregator web part.
Does anyone know how to do it?
According to this hotfix document, build 14.0.5136.5002 of the cumulative update package fixes this problem.
Issues that this hotfix package fixes
There is no such thing, but all you have to do is go to the web part and click the down arrow on the right tip side of it then click edit web part, after that click on URL and add the link for the site you want show in this web part.