How? I tried a nail in the hole 
Discussion
you should be able to poke a wire coat hanger in the hole
You may need a small flathead screw driver and twist it to unlock
I always use the ink tube from pens. Remove the tube from the pen, stick it in through the little hole in the photo and push to unlock the mechanism.
In the states, this worked for me for same problem, jiggled a bit while inside and unlocked, felt like a new superpower

This ☝️
You should just be able to shove it in the hole until it hit something in the middle. Then push. It should immediately unlock.
These are a bit tougher but you should still be able to break in fairly easily. Any sort of long pin or nail or eyeglass kit screwdriver should do the trick. 
If there’s space between the latch and the door frame you might be able to thread through a chord or cable tie to pull and release the latch - similar to this:
Our daughter wanted to be a spy for the longest time and MASTERED the art of popping these locks 😂. (Now, every morning I have to do this to get the teenage son up for school 🙄)
thats awesome 😂
I know the time has likely past, but I used to open handles like this with a q-tip that I stripped the cotton off.
