Why is it telling me the blood oxygen is not available in my region pls?

Not all features, particularly medical ones, are available in all regions. Check for you region by clicking on this link:

watchOS Feature Availability - https://www.apple.com/watchos/feature-availability/

akindele289 wrote:

Why is it telling me the blood oxygen is not available in my region pls?

Any device that diagnoses a medical condition is a “medical device”, and in most countries medical devices need approval of a government health agency before they can be made available to the public. When your health department approves it you will be able to get it. As pulse-oximeters are cheap and plentiful this should not be a major roadblock to measuring your oxygen saturation if you are concerned about it.