Do a reverse outline from what you have.
Read the draft and identify the scenes-- briefly.
Do it with a short phrase for each scene that will trigger your memory.
Put each scene/phrase on one card.
Or use excel or some other program if you must.
Then look at the collection of scenes and place them in the best sequence from start to finish.
I find cards easier for this. You may find cut and pasting better.
Now look for holes that are missing to make the set of entire scenes fall like dominoes when you read through them in sequence.
Also look for errors in scenes and fix those; as well as looking for needless side trip down rabbit holes which add nothing and toss those.
When you have all the scenes lined up in logical sequence with nothing missing and nothing extraneous, so they flow naturally from start to finish then you can start writing.
Of course use any existing text that you have that matches a scene that is still there, and modify it as necessary to fix problems you had identified. Fill in the missing scenes. And of course throw away the useless side trips that had added nothing.
You now should have a good solid first draft ready for editing.
After editing you can do the SPAG and fact checking or other needed clean up to have a finished novel.