Knowing how merging works, in this case it wouldn't really help. It certainly wouldn't make you the "owner" of the thread unless you'd posted in the start - if I do anything now, I'd effectively need to split the thread.
Thank you for responding. I know that I wasn't around when the thread was made, but a mod told me that it was possible to merge posts:
The only place it is possible is in Other Clubs, where if there's a club where the owner has become inactive you can ask Alternative to merge your first post in the thread with the thread's original post to make you the OP. Then you can edit the club from there.
Do you know anything about this? I was told to ask an admin because I'm trying to do it in Pokemon Groups rather than Other Clubs, but it's the same concept.