to finish an idea you started a long time ago, how do you put yourself back in the mindset that originally inspired the thing? i have this song idea based on a feeling of profound sadness that i've since gotten over, but now i'm kind of stuck going back to develop it.
gather more details about the original situation. maybe some things that you would not have even thought of including back then. if you can gather more details from that time, it should help jumpstart the process. you don't necessarily have to 'feel' exactly the same way, but if your brain knows you are pulling actual real details from the time period, then you will be more confident that you are for real in this process