Are you looking for something that will take audio as an input and automatically give you a MIDI as an output?
You can use pitch correction software like Image Line's Newtone or Melodyne to extract MIDI information, but the results will not be ideal for a UST.
If you want to practice how to tune from scratch, you can download an existing UST and clear the tuning. Select all the notes, right click and select Pitch. Click on the portamento checkbox until it's solid black, and click on the vibrato checkbox until it's empty.
Otherwise, the process of making a new UST from scratch is primarily based around being able to recognize the notes yourself, and you'll get much cleaner results from doing it by hand. Here in Songwriting resources you can find plenty of options for music software other than FL studio:
https://utaforum.net/resources/songwriting-resources.181/
One very important thing to do when you start working on a song is to set the project tempo to match and get the song lined up to the beat. Here's a website where you can tap to the rhythm and find the exact tempo of a song:
https://www.all8.com/tools/bpm.htm
Once you have the tempo set up, all of the note lengths should be nice friendly lengths (like quarter notes or eighth notes).