Need to change the "by" in "Posted on (date) by (user)"

I’m using Activello for a blog in Brazilian Portuguese. I’ve had success with everything so far. But there’s one thing I couldn’t change: the word “by” in the text that is below each blog post title: Posted on (date) by (user).
I’ve tried the theme editor and looked all over it, but I just couldn’t find where to change it.
I would be extremely grateful if someone could help me with that.
I’m attaching a picture so you can see what I’m talking about.

Hey there

You can use this method to identify files being used to render the page: How to Find Which Files to Edit in WordPress Theme