Do you need to measure VO2 max specifically? If your form of exercise is jogging/running, you will easily be able to tell if you're improving by tracking distance and time of your runs. If you want to be precise, you can e.g. race a timed 5k once per month under the same conditions. But if you're a beginner, you won't need that to be able to tell you're improving, just the feel of difficulty to maintain a certain pace will change noticeably.

As someone else mentioned, a classic poor man's test of VO2 max is simply to time trial a set amount, such as seeing how far you can run in 10 minutes, and use a calculator. So the same thing with extra steps.