How to upload file to relation in Strapi V4 (Repeat)

Questions and Answers
1
System Information
  • Strapi Version: 4
  • Operating System: Windows 10
  • Database: Postgre
  • Node Version: 14
  • NPM Version: 6

The documents don’t explain how to upload file to an entry very well. Can you help me with this how to upload to an entry??