Index.php

Could someone please help me with following messages:
While trying to run a job I received:

WARNING: File “/home/mysite/public_html/wp-content/uploads/index.php” is not readable!

Trying to make index.php readable I received:
550 Could not change perms on index.php: Permission denied

I posted this earlier on a wrong page and Daniël responded to change ownership to FTP-user. But that’s to high level for me. I don’t know how.

Thank you

https://ww.wp.xz.cn/plugins/backwpup/