How to hide date and author?

Add this to your custom css:

.post-byline {
display: none;
}

If you need a custom css area, you can install Jetpack.

Atahualpa has very good custom css areas and you will find all the custom css fixes at https://forum.bytesforall.com/forumdisplay.php?f=2 let me know if you can’t find it.
Cheers.