Before plugging in your Sonata board, hold down the SW9 labelled "RP2040 Boot", and while holding this button plug your board into your laptop using the Main USB.
A drive called RPI-RP2 should pop up on your computer and drag rpi_rp2_v0.X.uf2 into it.
This drive should automatically dismount once the file is transferred and remount as SONATA.
Currently the RP2040 firmware is available from the Sonata Systems releases, which ensures your RP2040 firmware matches the Sonata FPGA and firmware expectations.
The source & latest release for the RP2040 are also found on the Sonata RP2040 repo.