My understanding is that at this time, there is no way to update data from Excel, and it have it show up in Smartsheet. The Smartsheet Live Data Connector provides a read-only experience and is not able to write data into Smartsheet.
I would like to propose an idea for Smartsheet to be updated via Excel.
I'd extend this to requesting two-way integration with Excel. Even if it has to be refreshed as a semi-live integration, it would unlock a new level of usefulness. For example, I develop programmes in Smartsheet, but then need the data in Excel to be able to consolidate with confidential cost data and report in Pivot Tables. Yes, I know you can do all of that with multiple Smartsheets and paying a lot more for add-ons, but Smartsheets and Excel each have their own strengths, and if they played together nicely they'd both be able to do so much more than either can do now on their own.