The sounds you use are almost as important as the notes in scat singing, so it helps to practice them before you start improvising. If you listen to the singers like Ella Fitzgerald, Sarah Vaughan and Mel Torme, you will notice that they often imitate the sounds and musical lines played by saxophone and trumpet players.
This includes slides, bends and all kinds of expressions. For beginners, however, it is best to start simply and then gradually add more complex sounds.
All the vowel sounds are commonly used in Jazz, but when it comes to consonants, "hard" sounds like "T" or "P" are rarely used to begin a syllable, as they cause problems with microphones. "Soft" consonants like "D" and "B" are much more suitable. Try syllables like ba, bee, bu and bop, along with da, du, dee and dop. The possibilities are endless, but these will help get you started.
Listen to the recording and try improvising short phrases using these syllables with the Blues scale over the backing to the Blues in Bb.