Problem: Spreadsheets stored on OneDrive or Teams are showing dates in US format

Your OneDrive region settings need changing:
  • Log onto Office 365 via the website
  • Open OneDrive
  • Click on the cog on the top-right
  • Select 'OneDrive settings'
  • Click 'More Settings' on the left-hand side
  • Select 'Regional settings' under 'Region and Language'
  • Set the time zone to UTC ... London
  • Set the region/locale to 'English (United Kingdon)'

You may also need to correct any dates that you've already entered back to UK format. To do that, highlight the cells, right-click and select 'Format cells'. You should then be able to change the region back to UK. All new spreadsheets will appear in the correct format.