A typical wordpress .htaccess file with permalinks enabled looks like this:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
The bolded line in the sample above is the line to be edited. Change that line to this:
RewriteRule?./?/index.php?[L]
The new .htaccess file will then look like this:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ./ /index.php [L]
</IfModule>
# END WordPress
If editing the file via the FTP download method, save the file and reupload it to the public_html of the site. if editing the file via the file manager, save the file.
When the new .htaccess is in place, log in to the administrative dashboard for your wordpress install, and choose Settings -> Permalinks. Resave your permalink structure.
Any existing password-protected directories will function again, and new password-protected can be created as needed.