Download and install your microtonal tuning software. Open your tuning software and set up audio options for your computer, using "Options ---> Audio" or similar command. Download the Scala scale archive, and unzip it to a convenient place on your computer. Download your piece of music in ABC notation.
Look at your piece of music in ABC notation. Find the main notes used in the music -- the notes on the strong beats, not the weaker, "passing" notes. Make a list of the notes used in the music.
Count the notes in your list. If it has seven notes it can be called "7 -- note" or "Septatonic." Six notes is hexatonic, and five notes is pentatonic. Look up the notes on your list in the reference guide to Scottish modes, and find out which mode it is.
Open this mode in your microtonal tuning software. Drag the file from the Scala scale archive to the interface of your software, or use the menu options in the software. Open a virtual keyboard or similar window in your software and play the mode.
Practice singing or playing the mode on your instrument, making sure that you hit the right pitches. Don't worry if the pitches sound unfamiliar -- it may take time to get used to the mode.
Read the old Scottish tune from your ABC notation. Read the notes exactly as given, as old Scottish music is not very improvisational. Learn your tune so you can play it by heart and give it more life and feeling.