Yes, you’ll need to change your settings on the phone, not in the Limbo app.
The Limbo App uses the measurement units defined in your phone's settings.
If you want to change from metric imperial–kilograms (kg) to pounds (lb), you need to change the settings.
Navigate to your Phone Settings, select General, then Language & Region, and finally, choose your preferred measurement system. Additionally, you might need to update your location within the Language & Region section.
In case you reside in Canada, you will need to update both the measurement system, and your region to the US for the changes to take effect.
Once you've done this, please restart your phone for the new settings to take effect.