Changing attributes - .gitattributes

Welcome everybody,

we have Gitlab CE and need to change a behavior of gitlab, how it treats some file extensions.
For example when we want to download docx file from commit it has nice view with download window, but another extension is treated like txt extension although it’s binary.
I read here: , we need modify .git/info/attributes

Could we change it from Gitlab? I tried create in /var/opt/gitlab/git-data/repositories/xxx/yyy.git/info attributes file with proper content, then restart gitlab services but it doesn’t work.

We need to make text file to be treated as binary file to have download windows like this: