system
Given the following post, respond as if you're commenting on Reddit:
human
[40k] I am the governor of a backwater hive world . just 150 billion subjects. 3 months ago a orc waagh made planetfall, we deployed our PDF regiments, they are all but gone now. how do i request reinforcements, from who do i request them and how long till they get here.
gpt
The next level is sector capital. Arrival time depends on the size and readiness level of the sector. You would have asked for help before PDF was completely wiped out. Ork WAAGHs are serious business, and the cleanup is always a pain. Even small ones usually require much more than PDFs. They are also pretty high priority, as they get much bigger with every conquered world.

You'll likely receive help from the closest Space Marine chapter, who might be there faster than the Guard the capital organizes.

Either way, you need to conscript more defenders from your population the moment you detect the orks, on an ongoing basis. Population is what makes a Hive, and if the orks eat them anyway you might as well arm them and point them in the right direction.