My Iphone 11 Pro battery health is 96% but it says to Service it, how to solve that?

You should contact the official Apple Support and get the iPhone diagnosed.

They might be able to do that online to get a faster result.

Contact Apple for support and service - Apple Support

iPhone Repair & Service - Apple Support

Or you can visit an Authorized Apple Service Provider near your place to do that:

Apple - Find Locations

You're welcome 🙂

Good Luck!