I would really recommend doing the music theory course on here. It sounds complicated but it’s really not (after it’s explained).
So once you know the key you can work out the melody really easily as the melody will use the scale associated to the key ie G major scale.
Another way to work out the melody (for any song) is to go onto YouTube and watch an easy piano tutorial of that song. They will tell you which keys are pressed during the melody ie GCDGCD .. you can then Google the Ukuleke fretboard and work out where the notes are and play the melody 🙂
Honestly learn some theory it opens up a new world. I thought it would be really boring haha but it’s actually fascinating how it all fits together and makes learning so much easier as instead of having to remember patterns of notes for a song you already know them as they follow the scale patterns.
Enjoy 🙏🏻