Filling in CF83 employment details when company has been taken over

I have been working in Australia for the last 18 years and a couple of the companies that I worked for have been bought. Can you tell me what I should put in the employment details of the online CF83 form in this case please.

Hi,
If you do not know the previous name of an employer that has been bought you can put the current name of each employer, it is also important you include the exact start and end date of each employment.
Thank you.