

I don’t know if you did that, but for anybody struggling with those:
You’re supposed to put them together at an angle, so that the outer wall of the tins forms one straight line from top to bottom. Like this:
To open it you take them into one hand, hold them on the side where they form the straight line. Then take your other hand and gently smack against the part where the both tins connect with your palm
Here:
Since tin tins are hard to break (though not impossible I can tell from experience) you could also use a hard surface and more force if needed.
If they’re still stuck, let some warm water run on where they connect and try again. Although the drink might get watery if you take too much time.
Oh yeah, if you use them often enough you’ll get a feel for how much pressure you can use, I’m comfortable with using a little smack to close them, but I used to work in a cocktail bar, so I have some experience with them.