How to deal with burning out on a story

dude i get burnt out all the time without even starting writing. i have chronic writers block and executive dysfunction tho

but anyway, there's a number of things you could do! you could go through and edit what you have, and then continue writing.
you could keep note of all the things you know you want to edit in, like write them down somewhere, but just keep pushing on and trying to do better. with this one, you could honestly even write as though you had written all that character development and things, so that when you do go back, you know exactly what you want and where you need to start working from/to.
another thing i've seen people do is just completely revamp their plot/characters/premise, and start over. not that i'm necessarily recommending that, since you seen fond of what you have and interested in fixing it and keeping it, as opposed to changing it.

anyway, i hope this helps! and if you need any elaboration, do let me know! i feel your struggle lmao, writing is so hard, especially when you write over a long period of time and know that your older writing on the same project is so different

mood. i'm so bad about doing that lmao. carry a notebook everywhere and use it, even if the idea seems so obvious that you couldn't possibly forget it