I hope you are having an awesome weekend so far! Where were you trying to change your start date? At first I thought maybe your Fiscal Year but then quickly realized that wouldn't make sense because we are only dealing with January so I thought maybe it was in regards to something else.
In most areas inside QuickBooks Online we will have a filter icon in which we can set different dates. For the most part date change options are in the top left hand corner of transactions or reports.