You can easily find your FTP details by opening your cPanel and clicking on FTP Accounts:
If you created an FTP account before (it can be done on the same page above), in the FTP Accounts section you will see presented with these buttons:
Button to change FTP account password
Button to change FTP account quota
Button for deleting your FTP account completely
Button for checking your FTP details
Your FTP details should look similar to these:
NOTES
If your domain is not pointing to Hostinger by nameservers, the FTP server address will not work as a host for an FTP connection. Replace it with your account's IP address
FTP is not available for websites created with Hostinger Website Builder