Postponing job interview because I need more time to study for it?

Hi

How can I convincingly postpone a job interview if I realised that I need more time to study the topics that are relevant to the job?

I've got an interview appointment but during preparations I clearly saw that there are several main topics where I need to get deeper into (crucial technologies for the job) in order to be ready. It will take me 4-6 weeks to become proficient in those areas.

How can I postpone a job interview in such a case? I can't tell them the true reason.

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