Why my battery health is increased 89 to 91 plzz reply

Do you have an iPhone 11? Have you recently updated the version of iOS? If so, see the article below.

About recalibration of battery health reporting in iOS 14.5 - Apple Support

If you have iPhone 11, there was an update released in iOS 14.5, which recalibrated battery health on iPhone 11 to be more accurate. That would likely explain why your health went up.