Btw for OP, unless you have read the other numerous threads about this subject, Dave already mentions but cannot be emphasized too much that the usual reason for a lousy 1 min power number is the lack of dedicated testing.
Typical number I see in my group rides for 1 min is ~550w but I can put out over 800w which gives you the picture of the difference between dedicated test and a road race/ride. That is just so horrifyingly gruel thing to do that I don't want to do it many times a year.
But how to do it: find about 1 km long climb, not necessarily too steep though. One which limits your speed but where you can still ride without wrestling with your bike.
Sprint all out and sit down once the cadence is not controllable out of the saddle anymore (that should be anywhere between 10-20s). Spin furiously. Concentrate on spinning faster and faster with rage. Around 40s you will be absolutely spent. If you are on an adequate uphill (or switch gear but that is going to cost you some time and concentration, uphill is better) you can stand up and try to get the last bits out of your legs which isn't much though. Prepare to see stars and vomit 😄
I think the numbers for 1 min in power profiling are from Kilo riders so uphill and standing up is a bit of "cheating" but on the other hand if you do not train specifically for Kilos you cannot get all out of yourself on flat like they do.