I found a better quality version of a post i uploaded and... you know... How do i request for a replacement?

The feature is fully public yet meaning only certain people have access to it. You can see it on peoples accounts as "replacements beta" under permissions.

As far as I'm aware the only option if you don't have access to it is to send a DM to someone who has (e.g. staff members) and asking them to submit the replacement.