How to connect 2 domains to 2 distinct sub-site?

Hi there,
On my hosting provider I've got:
3 domains
Of which 1 domain is used as main for the WP Multisite Sub Domain install.
2 subsites.
I'd like to "connect/map?" the 2 other domains to their corresponding subsites. Do I need domain mapping to do so? Is it possible an other way (not sure I have a dedicated IP)?

Please advise,
Thank you
Julien