The star shape is in the spindle so the entire spindle will need to be replaced
As suck it is now a throw away item ( makes a good drift ) so you can grab the end with a pipe wrench or weld the blade , which is also throw away to the spindle .
Once the top nut is off the spindle drifts out to the bottom
While it is out, replace the two bearings as well 6203 top & 6204 bottom.
Get them from a mower shop or bearing shop to make sure you do not end up using shopping trolley grade bearings that are all over the web cheap cheap.
Leave the housing in place.
They generally break when you try to remove them.