LoadDataInfile mysqld file access


I am trying to solve the LoadDataInfile warning in System Check. I am now at the step:

give the process mysqld executable-access (+x) to files in path/to/piwik/tmp/assets/* and all parent folders.

But how can i do this? Can’t find it anywhere and not in the docs. How can i do this?
My system is running CentOS 7 with MariaDB.