My computer's system & gaming sounds are too loud. Problems arose every time I need to reconnect speakers with the case. I don't remember how I solve it last time.

No, adjusting system volume has 0% effect, it's equally too loud at 1% and at 50% At current setup. I had to change sound provider to mute the sounds, form too loud sound provider, to provider that brings no sound at all, even at 50%.

So, I have to find way to game with normal sound.

Using win10, comp is recently built and I have Nvidia graphic card. Not sure on spec, I have to check it out.
Speakers have volume control, there's no special software and yes, I altered that icon on taskbar that controls sounds.

So many words and still nothing about your OS or HW specs. *shakes his head in disbelief*

edit: also, what do you mean by "I need to reconnect speakers with the case"?

No information.

Does your speakers have a volumne control?
Does your soundcar have its own software, if so have you altered sound volume there
Have you altered sound volume in windows

I fixed the lack of info in OP. When I mean reconnect speakers with the case, I mean basic removing and plugging in usb from computer case.

Your speakers connect by USB? Then they are effectively their own sound card and should have a separate volume control in the tray. The one you're adjusting that's having no effect is probably the one for your motherboard's soundcard.

Ah, USB sound... I have same problem with mum's computer, too loud. I need to activate the USB speakers in Windows and then set volume to 1% ... After that I must NOT use the earphones or I will have to fix the sound settings again. Maybe my little story can be of help.