I can’t able to set up mobile data in my phone for my Apple Watch series 6, where as earlier I did it enabled for the same watch by my same iPhone 11

Set up cellular on Apple Watch - Apple Support

Before you start

• Make sure that you have the latest software on your iPhone and your Apple Watch.
• Check for updates to your carrier settings.
• Make sure that you have an eligible cellular service plan with a supported carrier. Your iPhone and Apple Watch must use the same carrier,* and you must be within your carrier's network when you set up cellular on your watch.
• If you have an enterprise or corporate cellular service plan, check with your company or carrier to see if they support this feature. Pre-paid accounts and some older accounts aren’t currently supported. To make sure that your account is eligible, contact your carrier.