Hi, I am Van. I'm an Independent Advisor and a Microsoft user like you. I'll be glad to help you today.
Are you using the latest update of Windows? Press Windows Key + R, then type winver on the run command to know what version of Windows is installed on your machine. In the latest version of Windows which is version 2004, Windows Defender is now called Windows Security App
To know where is the manage setting, click the Windows Defender or Windows Security icon in the system tray or click the start menu then type Windows Security. Once you are in the Windows Security dashboard click Virus and Threat Protection or the Shield Icon. Scroll down and select Manage settings under Virus and threat protection setting.
Please let me know how it goes. so I can further assist you if are still having trouble finding the manage settings
Best regards,
Van