Google Sheets fix errors and optimise speed and user friendliness

I need a good google sheets technician to fix a spreadsheet we have moved from an old version of Microsoft Excel to Google Sheets. The spreadsheet has error in the formulas now and needs to work faster. i.e. open / go to the current date section rather than old date. When switching between sheets/tabs it should not got back to the start date.
Good communications and live chat whilst working on this will be important.