I agree with Bill. My job-related hobby (other than ukulele playing and motorcycles) is making play along videos on YouTube based on existing audio (versus making a cover). My process is to determine key, and then see the existing chord arrangements, and then to change keys (if necessary) to make things more ukulele friendly and then to sort out the actual chords. Some songs have multiple solutions, and sometimes people can listen to the songs and hear different things.
For the sake of your own learning..since you’re going backwards, would be to determine the key, see if the online charts match it (that could be the big issue), tranpose the written chords if necessary, and work through the song. When you have a solution or you get stuck, post what you have and you’ll get at least a few opinions on what might work.