I usually write down everything I need to figure out on a note on my phone and if there is a deadline or time I need to figure it out by. Having it all down means you have an easier time letting go of it since you can just keep checking your list. It also seems like less things to overwhelm you than you initially think there are when they are all down on paper as words.
If you are already close to feeling overwhelmed, I would do something that is repetitive or that helps you calm down like cleaning or arranging something that is out of place in your space, or pace around for a while to let go of some of that pent up tension. It tends to work if you are stressed or angry from feeling overwhelmed. Talking to someone through it also helps, or getting help with your situation.