I think your best bet would be to do a fresh install (to get rid of any original arch package/remnants you’ve installed previously) and try to establish a LAN connection to be able to use Manjaro’s package manager(s) and tools such as mhwd for kernel installation (and updating grub etc).
I’d also recommend to at least get familiar with Linux’ directory structure and basic terminal commands, since this is where the real magic happens. Here’s a collection of useful links: