Proof of willingness to work. UK Ancestry Visa

How do you prove you are applying for jobs for your UK ancestry visa when you register with one of the companies ie Reed, Indeed etc and it asks if you are allowed to work in UK. I originally wrote "no" and was not allowed to apply or the jobs?? Is there another way or do I just write that I am allowed knowing my application will most likely get approved based on both my mother and grandmother being born in the UK.