What is Percy Shelley's prayer to the west wind?

The speaker prays to the west wind to make him its lyre.
A lyre is an ancient musical instrument, kind of like a small U-shaped harp. Lyres had special resonance for poets such as Shelley, as in Ancient Greece, poems would often be sung to the accompaniment of a lyre. This is where we get the word "lyric" from, as in the lyrics of a song, or lyric poetry.
Shelley invokes the west wind as a metaphor for his own art. He hopes that the wind, his poetic sensibility, if you will, will stir up his dead thoughts like withered leaves and drive them across the universe to quicken a new spring—that is, spark his imagination into life. Shelley yearns for the west wind, his poetic faculty, to play him in order to create great poetry, just as the wind plays the lyre to make sweet music.
https://www.poetryfoundation.org/poems/45134/ode-to-the-west-wind