I already have a tourist visa, that I have used for three months traveling in Australia. Now I want to go back on a Working Holiday Visa. Do I need to cancel my initial tourist visa before I apply for the Working Holiday Visa?
No, you do not need to cancel your current tourist visa. If this is your first application for a Working Holiday visa, you must be outside Australia when you apply and when the visa is decided.
As part of the application, among the question asked:
Have you have previously been to Australia, applied for a visa, held or currently hold a visa for travel to Australia (including a Working Holiday visa)?
Give full details including type of visa(s), place(s) of application and date(s) of entry to Australia (if applicable)
That information and your passport details are sufficient for the government to nullify the tourist visa as it grants the new, Working Holiday visa.