Your widget settings can be accessed by logging into your Groove account, click the Settings icon in the far left menu bar. In the Integrations (Legacy) section, locate the Support Widget app and click Settings. Here you will see a list of the widgets you have added to your account and you can access the individual settings by clicking the gear icon.
Under "General Settings" you will see a dropdown option to "use default color scheme" or "use custom color scheme."
When you select custom, a color picker interfact will appear where you can change the colors of your widget to match your brand.
Just make sure you publish your changes when you're done!