Treadmill advise please

When you say you struggle and get out of breath quickly, can you tell us what you’re doing and what kind of timeframe quickly is?

Are you starting to walk on the treadmill and getting winded after a couple of minutes?

Are you trying to run at 12 mph and can’t keep that up for long?

If the first, do what you can. If that’s 2 minutes, do 2 minutes. If you can do another 2 minutes after a bit of rest, do that. On days you feel stronger, add a little time. Eventually, over the period of weeks and months, you’ll find you can go longer every time.

If it’s the second, slow down (and follow something like c25k if you want to run).

If you're starting out right from the beginning the first thing to do is work up to being able to walk for 30min at a fairly brisk pace.
I could only just manage 5min at 2mph to start with, so I started there and added 1min every time I went to the gym until I could walk for 30min.
Then I downloaded the c25k app and instead of running in the run intervals I walked faster. And I kept repeating until I could walk for 30min at 4mph.
Then I started running in the run intervals, but very very slowly. The best advice I got was to slow down, then slow down some more. I was barely faster than when I walked but was running. Once you can run for 30min then you can start working on speed and increasing distance.