When I used command prompt it gave me 'Invalid switch - -r/s/d' message. Through file explorer I couldn't change.
You're missing the spaces between the arguments:
attrib -r /s /d
However, you are wasting your time if what you're looking at is this:
.
.
If you look at other folders, you will see that they all have that same "indicator". It's perfectly normal and essentially meaningless and has always been that way. It will not cause any problem.
To be clear, that "indicator" does not mean what you think it means. The folder itself is not read-only. You can verify that at a command line with the attrib command (with just the folder name as the only argument).
It's actually an operational item rather than an indicator. It always shows the black box indicating that one or more files in the folder may be set read only. So, it really isn't any kind of indicator at all. But if you check the box, it is a command to tell Explorer to make all files in the folder read-only (it will ask for confirmation). It can also be unchecked to make all files in the folder not read-only. But it will always display a solid box!
Whatever issue you're having, it's not caused by this. Please tell us what actual problem you're having that led you to believe it was this "indicator".