Hi and welcome to the forum 
Please add a overview of your system (see how to provide good information) to the post, it had some details most users who support others know what to look for in your case and lend a hand.
One thing to start to check is the following: Since booting into manjaro works, you maybe need to tell grub to find your windows install to boot from.the output of sudo update-grub should have 2 lines that look like this on a recent install:
Warning: os-prober will be executed to detect other bootable partitions.
Its output will be used to detect bootable binaries on them and create new boot entries.
If you have the output below:
Warning: os-prober will not be executed to detect other bootable partitions.
Systems on them will not be added to the GRUB boot configuration.
then you need to enable os-prober, the easiest with the following command combination in a terminal: echo GRUB_DISABLE_OS_PROBER=false|sudo tee -a /etc/default/grub && sudo update-grub
I probably won’t be of much further use to you since I will be away for at least a day. For a first post, 
it sounds like a learning journey, i hope it is educational 
A dual boot guide that on this forum is a good read / guide to follow along. (no personal experience with dual booting)
One way to start over with windows and make a rescue usb drive is described here