The Mk3 was sold with two variants at each trim level. If yours is a "Navi" version (which came at a premium price), you should have the onboard satnav. If not, you haven't got it and I'm not sure it can be retro-fitted (ask a Honda dealer). If the salesman told you it was there or could be enabled yourself, then you have a case against them for misrepresenting the product.
There are reports of people downloading a nav app to the infotainment system, but it involves hacking the OS to remove legal safeguards such as enabling viewing of videos whilst driving, and I'm not really sure it offers many advantages over simply using a phone (in a suitable holder, of course).
Not exact.
Jazz 2015-2018 was sold in 3 trims, S, SE, EX: the two upper levels, SE and EX, could have the infotainment system with or without navigation system, in case of NAVI level the unit had also DAB radio receiver, cd player and shark fin aerial.
The two units, standard and navi, are different both in hardware and software, the NAVI has different settings and a GARMIN android app for the sat-nav:it's not possible to add this Garmin app on a standard unit, even if the software looks the same of the navi level.
But....
Even if the standard level has no sat-nav apps, it has the navigation hardware and the car has the satnav aerial. So it's possible to add another satnav android app such as Sygic, Copilot, Waze (not the Garmin as I wrote before), legally removing some software locks in your unit.
How to do this: follow the turorials here
https://www.cmdroid.com/ download your apps and install them.
PS the website is set for HR-V brasilian models, so left hand drive, but apps are the same for all Jazzs. Only the unit firmware is different.
Installing apps is possible only for unit firmware RC 6,1 or earlier, check your version.
Honda app center, as far as I know, has been set off.