I cant do it because i dont know anyone in bios modding. Help me if you can:)

intel z390 chipset (coffee lake)? or msi z390 series?
need more information,especially your cpu name and or cpu id/platform id

for spectres: see here if your cpu is on the list; intel cpu microcode updates
as Microsoft states; "This update for some select products (CPUs) is available through Windows Update. It will be downloaded and installed automatically"
meaning; possibly you have it already if you are updating your windows regularly.to make sure you have it,you need to search for Mcupdate_genuineintel.dll in your windows folder and look for it's date and size.if it matches the date and size given in the page,you are good to go

for meltdown: follow this guide get the latest software for your management engine and upgrade it's firmware

if there are no microcode and/or management engine firmware update available for your setup (either through bios update,bios modding,windows update or management firmware) you may be still protected if you are using latest windows 10 (microsoft safeguarded through some registry edits in place,comes with reduced performance)

you can check it with this little software called Inspectre
and you can remove those registry safeguards with this little tool if you are properly protected in order to gain your lost performace back)