External HDD always spinning

My External HDD is loud due to constantly spinning, is there a command to fix this?

Please tell me step-by-step (noob here)

Thanks in advance

On which device do you have the problem?

I had the same problem yesterday on a friends rpi3b+ with different hdd’s and usb adapters on dietpi buster and raspbian stretch.
There it seems that an mouse which was connected to an usb hub on the keyboard caused the problem (many usb reset messages in dmesg). But after unplugging the mouse I always needed to reboot the raspi to fix the continuous hdd spinups