private String getExtLibPath() {
		String extLibPath = extLibPathTextField.getText();
		if (extLibPath != null) {
			extLibPath = extLibPath.trim();
		}
		return extLibPath;
	}
Pop up the data tree dialog so the user can choose the external program.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/symboltree/EditExternalLocationPanel.java