MagWLED-1 comes with a USB-C connector which can be used for flashing.
For pre-compiled firmware with default MagWLED-1 pin configurations out of the box, visit https://install.magwled.com/. This page also includes SoundReactive versions of "vanilla" WLED and higher performing MoonModules versions.
MagWLED-1 is, of course, also compatible with recent versions of WLED and you can install those versions directly from https://install.wled.me/.