The small battery (that is now flat) is definitely 12 volts.
You definitely need a jump start from a 12 volt battery or booster pack.
The Toyota built-in jump start point is inside the fuse box that is under the bonnet - it is on the passenger side. If you unclip the lid (clip is on the front leading edge), then you can remove the lid completely. You can then see a red rectangular plastic clip, about 2.5 cm wide, towards the back of the fuse box. It hinges at one end and has a small clip at the other end that you can operate with a finger nail, and then pivot it up. (There is a map of the fuse box underneath the fuse box lid, btw.)
This reveals a vertical metal blade. This is your positive (red lead!) attachment point from your positive terminal of your other battery. The black lead, from the negative (-) terminal of your other battery, can be connected to (clamped around) one of the suspension mount nuts that is just beyond the the fuse box, a bit nearer the windscreen.
Good practice is to put the earth (black) lead on last and take it off first when done, but this doesn't really matter. The Auris hybrid won't draw much power before it's able to start up, so it won't take much juice from the other battery.
The potential problems from this procedure are overplayed, just don't get the cables connected wrong - positive to positive, negative to negative is what you need. (But using your car to jump start another car is a different story - don't do it.) It's best to have the other car ticking over whilst you are doing this, so you don't flatten that battery too. When your car has successfully started, remove the earth (black) lead first at both ends. Then the positive (red) lead at both ends.
Afterwards, It's definitely worth operating the car in 'Ready' (even if just sat on the drive) for an hour, or even more if you can, you don't have to drive fast or far, just have the system in 'Ready', on this car, it will charge the 12v battery at the same speed, regardless of how you are driving it. It is almost essential to trickle charge the battery overnight at the soonest opportunity, just to give yourself the best chance of stopping this happening again.