How can I learn German in one week?
If there is way to listen and talk that will be better.
If you want to learn some formulas as Guten Tag, Auf Wiedersehen, Danke, Bitte, Ja, Nein, and so on, I think you can do it in one week. Whether you can call this "to learn German" is another question.
There are books available that promise "Learn German/English in thirty hours" - that is throwing sand in your eyes. They mean thirty lessons of German/English and contain nothing but a basic survey of the basic grammar of a language and perhaps a vocabulary of 500 to 1000 words.
Don't fool yourself. The study of a foreign language is always a study of several years, no matter how many people tell you you can learn German in a week. They want to sell you something. And they promise you the moon.
And studying a foreign language has its price. You need good tools for learning a language. A dictionary for beginners, a bigger dictionary, a good grammar for beginners, course books, audio material, texts for beginners - all that has its cost. And when you engage a private teacher, he has his price too. Good things cost money.
And forget "Crash Courses". What you learn in the one week of a crash course you have forgotten in the next week. Some people think learning a language is another person that fills the language in their mind. No, learning a foreign language is a technique you have to learn for yourself and most people who learn a foreign language know nothing about the technique of learning a language. It is an active thing, not a passive thing that others do for you.