You mobo specs list:
- 1 x 4-pin CPU fan connector
- 1 x 4-pin water-pump-fan connector
- 4 x 4-pin system fan connectors
- 1 x 4-pin RGB LED strip connector
(https://www.msi.com/Motherboard/B350-PC-MATE.html#productSpecification-section)
meaning you have plenty of fan connectors.
Unplug your fans from the molex connection (shut down your pc first of course), then connect them to the 4 pin system fan connectors (download manual here https://www.msi.com/Motherboard/support/B350-PC-MATE.html#down-manual, then go to page 22, they'll be labelled SYS_FAN 1 through 4).
Download from
https://www.msi.com/Motherboard/support/B350-PC-MATE.html#down-utility
a utility called command centre. You technically don't need it but it's nice not to have to go back into bios to adjust your fans every time you want to nudge the curve up or down.
Anyway, first after you connect the fans, load into bios then from there, select each of the system fans (don't touch the cpu fan), and select DC instead of PWM. You can adjust temp/RPM curves yourself or let system optimize it. Then once you start up, start the command centre, and from there you can access those fan curves and further adjust if you want them lower/higher while you're gaming or doing stuff. Just be aware that for those adjustments you apply in command centre to stick, command centre has to be loaded, and whatever profile you created, also has to be loaded. Otherwise it just reverts to bios settings.
I'd also get something like HWMonitor which will let you keep an eye on system temps and rpm of all the fans, so you have better overview when adjustment is needed.