How can Clean the SFDC opportunity data for a team of 5 sales users, around 1000 opportunities have either missing or incorrect field data. what is the one by one steps. Please help me

1. Create a report on opportunities dont forget the opp ID field.

2. Add the relevant field you consider important to check E.g. stage, billing contact etc.

3. Export as CSV or Excel

4. Give it to person that can fill in valid values 

5. Use workbench or data loader to Update or upload data