Note
The instruction below is for Modern SharePoint pages. If you use Classic SharePoint pages check this instruction.
If the web part is not configured yet you need to start the configuration as it is described in the quick web part configuration guide.
If you need to change settings of an already configured Web Part, you need to perform actions below.
Open your page in edit mode.
Click pencil icon at the left side of your web part. It will open property pane.
Click Open Config Wizard in the property pane.