I find that this helps when anxiety gets in the way: I identify it (instead of letting it endlessly cycle unnamed in my thoughts), then I give myself permission to let it go for the immediate moment by saying "not right now, I'll address it later". And then when I have a few minutes, I sit down with pen and paper to write down the anxiety, the emotions and issue it is coming from, and some possible solutions to the source problem. I find it converts it to problem-solving rather than the spinning anxiety that ruins my day. I hope it helps you too!

The tenets of Stoicism and Taoism are useful to help with thinking.

Meditation is a good tactic, and plenty of resources here:
reddit.com/r/meditation

I started using Headspace (a meditation app) a few months ago and I am amazed at how much better I'm able to handle everyday life. I also tend to overthink, think in circles, and have a lot of anxiety. Headspace is free for the first 10 days and then is subscription after that. I am a pretty cheap person and usually don't spend money unless it's something that is necessary in my life such as food and rent. However, after the 10 days I realized I was getting a lot of benefit and I went ahead and bought a year subscription to headspace. It has made a huge positive impact in my life. Headspace isn't the only answer, though. There is a lot of information on meditation out there and most especially meditation with mindfulness. I highly suggest it.

i use headspace too... its great for helping u sleep... cant afford to subscribe, so i just do 10days then start again...