I'm currently trying to setup a subway rail, but there is no options in the stations settings to the underground transition. i only see the trainstops on either surface.

Picture for clarification: https://ibb.co/tM6s6rmS

Do you use other mods and did you place the opposite subway?

Figured it out. They need to be placed in the right direction and placement.

Would be nice if there was some tips and tricks explaining how these substation transitions should be placed.

Aren't the markers sufficient that appear when having a subway in the cursor?

The markers do not show any directions.

the markers also didn't appear at first and i only found out because i was trying to move the subway around to make it work and suddenly the marker appeared.

The markers do exactly show where and in which direction to place the opposite. They can ofc only appear if you already placed a subway to know where the counterpart has to be