OK lets see we have the splitter here:
https://gbatemp.net/threads/legal-nsp-splitter-for-fat32.520213/
Then once you split them it'll be files xx.00, xx.01, xx.02 etc.. in a folder. Copy that folder to nsp folder for tinfoil.
Then you want to use the latest NXShell
edit: (grab from here, the one included with kosmos does not have the option to set archive bit, i think):
https://github.com/joel16/NX-Shell/releases
Enable developer options in NXShell, then find the folder you made and copied on the SD card. Set the archive bit using NXShell.
Then tinfoil will see the folder as a installable file.
Might wanna update your FW at some point (ChoiDujourNX), as I am sure some games wont work.
Also kosmos can be found here: https://www.sdsetup.com/console?switch