Hello Dogboz,
Thank you for posting in the Apple Support Communities. We understand that steps on the Apple Watch are showing in kilometers unexpectedly, and we're here for you.
When you're in the middle of a workout in the Workout app, you should be able to highlight the metric that's most important to you. You do this by raising your wrist, then turning the Digital Crown. Check out the section "Track your progress" in the article below to learn more:
Use the Workout app on your Apple Watch
If this issue doesn't seem to be expected, then there are some steps you can take to further isolate the issue such as restarting both devices and ensuring they're fully updated.
Restart your iPhone
Restart your Apple Watch
If an update is available, we suggest having a current backup to iCloud or to a computer, first.
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
Update your Apple Watch
If this concern continues after taking the steps above, our resolution is to contact Apple Support directly. Depending on your region, you may be able to reach them here:
Get Support
We hope this information is useful. Kind regards.