There is an idiom, to be in the swim (of things), or to get (back) into the swim of things. This means to be or become involved involved in a certain activity or event. Or even just activities in general. I have not studied German in many years, but soon I'll be back in the swim. I was sick for a long time, but I hope to get back into the swim of things soon. (This can refer to getting back into the normal pace of life in general, or to something specific, such as one's job.) It didn't take her long to get back into the swim (of things) once she put her mind to it. (Put one's mind to = concentrate). To be out of the swim? I don't think this is an idiom. But it makes sense, since it seems to be the opposite of "in the swim." But a better phrase might be "out of practice." I was so out of practice when it came to my job that it took me a couple months to get back into the swim ( of things). = to get back to my accustomed performance at work. But nowadays, the idiom "in the swing of things" is more common than "in the swim (of things)," at least in my part of the USA. In this case, we almost say "in the swing of things," not just "in the swing." But, yes, "in the swing of things" is more common nowadays, as compared to "in the swim (of things)." And the meaning is not exactly the same. In the swim (of things) = to participate in an activity in the swing of things = the usual way that something is done To get back to the swim of things can mean to get into the swing of things, so the idioms can be used to express the same thing.

I've heard it used on occasion, usually in a book or something. Its not a common phrase that people really use though. An example might be, "He has been ill and out of work for a while, but he should be back in the swim of things soon."