How do i show related items in a module position like a sidebar?

Unfortunately K2 Content does not offer this functionality.
You can look for an extension like this in the JED or the KED.

I'am looking for that, but did't find some.
Do you have suggestion

There was a module called BNR related items, or something similar.
I have not used it, nor do I endorse it, but several members of the community have used it.

You can look into it, and see if it offers the functionality you want.