How to update Additional Boards Manager URLs

Development Tools IDE 2.x
4

The additional board manager URLs are stored in the file C:\Users\yourUsername\.arduinoIDE\ arduino-cli.yaml.

You can safely delete that file or you can edit it with a normal editor.

  1. If serial monitor is open, close it.
  2. Another way seems to be to open an new instance of the IDE and close the one that is stuck.