Responses
If you are referring to the status that appears when you click on a story, I believe you have to file a request of some sort to someone who runs the site in order to change the status from ongoing to completed. I’m not an uploader though, or at all familiar with this stuff (just something I think I read in passing one time) so take my words with a mountain of salt ( ̄∇ ̄")

how do we mark a manga/manhwa as completed when it has ended? i hate it when i read something, binge it, and then find out it’s not even completed after like 60 chaps in
it makes searching for a good read so hard because sometimes some stories ARE completed but isn’t even marked as complete!