How do i change steel band it got discoloured

Change your Apple Watch band - Apple Support

Hi

Apple advises in the User Guide that band colours may vary or fade over time.

However, if you are concerned about a potential manufacturing defect, contact Apple Support (mail-in service may be available) or make a Genius Bar reservation with a view to having your band checked under warranty:

https://www.apple.com/support/watch/contact/