If you try to patent something that already exists (whether it has a patent or not), you will need to modify the product, method of use, and/or method of manufacturing enough to make it your own.
The prior art of something already patented or being produced stands in your way, but it isn’t impossible. In fact, there’s almost 50,000 patent results on Google Patents for “bottle openers.” So it’s not like the first person ever got the patent and nobody else could, they all just had to modify the idea somehow, in a “non-obvious” way. Non-obvious meaning you can’t just change the color of a bottle opener and expect to be granted a patent. Hope this helps.