Preview is only possible in Admin Tools for Joomla where we create a .htaccess file from scratch.
On WordPress we can only add / manage a section of the .htaccess assigned to our software. As a result there is no preview.
The reference to the Preview button in the documentation is wrong. This feature does not exist. Thank you for pointing it out.
Regarding your .htaccess file, pleas try to temporarily give it 0777 permissions for Admin Tools to be able to write to it. You can then change its permissions back to 0644.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!