You may want to get a book, or failing that, find a website that describes the process.

I used to use a plastic 35mm film canister, with a pin hole in the lid and the bottom cut out. Of course, this requires you to actually find such a thing lying around, and since most people no longer use film...

Anyway, the film container fits in the focuser, you look through the pinhole, and you can use that to line up the secondary mirror.

But a book or website that gives the steps is what you really need.

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"Arrrgh, the laws of physics be a harsh mistress!" -- Bender