You can restore your WordPress .htaccess file, in this way:

• Delete the old .htaccess file
• Create a new, blank, .htaccess file in your WordPress directory via FTP or SSH
• Change permissions to 777 for it (if you use Linux server)
• Log-in to your WordPress dashboard. Navigate to Settings menu -> Permalinks -> update ‘Permalink Settings’ (choose any option there).
• When done, change the .htaccess permissions back to 644.