Hello,
first to do- the secondary mirror must be centered and round in the focuser. To check, clamp a large sheet of paper crosswise in the tube to prevent it from looking at the primary mirror. For checking/adjustment, a Cheshire or a Concenter is helpful, or in a pinch, a cap drilled through the center of the focuser.
Then align the secondary mirror to the primary mirror. The HS must be seen centrically, this can be seen by the retaining clips of the HS or its edge.
The third step would then be to align the HS with the help of its adjustment screws so that the center marking is in the center of the image. An alignment laser can also be used for the last step.
Helpful links for this-
http://www.seeing1.de/2a_justage.html
http://www.pteng.de/astro/justage/justage.htm
and for translation - https://www.deepl.com/translator
best regards Stefan
