I need a prayer an ancient greek said or may have said to Euterpe, the
Greek Muse of music and lyric poems.  Thanks!

This famous prayer to the Muses appears in the prologue to Hesiod's "Theogony":   

"Farewell Zeus's daughters, and bestow the song that beguiles.
 Make known the eerie brood of the eternal Immortals
 Who were born of Earth and starry Sky,
 And of dusky Night, and whom the salt Sea bore.
 Tell how first the gods and earth came into being
 And the rivers and the sea, endless and surging,
 And the stars shining and the wide sky above;
 How they divided wealth and allotted honors,
 And first possessed deep-ridged Olympos.
 Tell me these things, Olympian Muses."   

This could easily be adapted into an invocation specific to Euterpe.