Theoretically nRF Toolbox should work. Use the DFU function. Sadly I can't confirm because I can't get the app to launch on my vintage iPad (as in 'really old'). Probably the wrong flavor of Bluetooth hardware. But on my much newer Android phone the app works great.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Theoretically nRF Toolbox should work. Use the DFU function. Sadly I can't confirm because I can't get the app to launch on my vintage iPad (as in 'really old'). Probably the wrong flavor of Bluetooth hardware. But on my much newer Android phone the app works great.