How do get Excel spreadsheet to update?

Jwww-ong 

Hi Jason - welcome to the community!  We're glad you're here.

The file you have added to the channel in Teams is 'the' file.  You can make updates to it in Excel when you aren't logged on to Teams and you can locate it in SharePoint.  When you are in Teams, you can make edits directly in Teams, via the web version, or you can choose to open in the native app and make edits or updates there.

You might be working on two different versions.  For instance, if you make edits to a doc on your desktop, that's not going to edit the version you uploaded to Teams.  If you have two versions, you'll want to delete any other version and just work off of that master spreadsheet you want to have updated for our team members.  

Again, you don't have to be logged into Teams to work on it - it's a file stored in SharePoint that is accessed by Teams.  

Let me know if I might be misunderstanding your question but hopefully that will help you.