How to change the decision on default language for file extension?

[ghost]

I accidentally chose Visual Basic for .bas file extension and it will treat .bas files as Visual Basic without asking me again.

[SpartanJ]

You can't 🥲. I should add an option somewhere, this needs design. Let me think about it.
Meanwhile you can edit the config file manually.
Open the ecode config file: config.cfg, that it's located at the configuration folder path:
Linux: uses XDG_CONFIG_HOME, usually translates to ~/.config/ecode/
macOS: uses Application Support folder in HOME, usually translates to ~/Library/Application Support/ecode/
Windows: uses APPDATA, usually translates to C:\Users{username}\AppData\Roaming\ecode\

Search for: [languages_extensions] and remove the block or edit it (it will have something like bas=visualbasic. Also edit it with other editor than ecode, because on ecode close it will override your changes 🤔 .

[ghost]

I should add an option somewhere, this needs design.

You don't need to. I'm OK with the current behavior. Still better than asking me each time I open a .bas file like on other editors. I'm not afraid of editing config files, either.