I give you 3 options and you google them and choose the one which suits you the best. 1. Change the boot order in your bios (Mint drive first) 2. Install package ‘os-prober’ and then update-grub (Win10 will appear in Grub) 3. Install rEFInd to replace Grub and choose everytime which OS you want to boot (set timeout by yourself). Warning: theming the rEFInd is known to be addictive.