I cannot find the For authors page in the panel

The text of the For authors page on the public site is a guide whose address is yazarlar-icin. You edit it among the guides on the Pages & policies screen, not on a separate screen.

1. On the Institutional content → Pages & policies screen, go to the Guides tab.
2. Open the guide whose address is yazarlar-icin.
3. Edit the text, save it and publish it.

If there is no such guide, select Guide in the New page menu and enter yazarlar-icin in Address (slug). Until the guide is published, the page opens with a built-in text. In every case, the page also lists the ways to submit to the published journals.

A journal's own author guidelines are in the journal profile and are described in Setting Author Guidelines and Review Criteria.