I want to remove battery message

You chose to not have Apple or an Apple Authorized Service Provider replace the battery in your iPhone. They don't have access to authentic parts, so you'll have to live with the message. After some time the message will stop appearing on your screen, but the phone will ALWAYS show it has unauthentic parts installed. There is no way to get rid of that.

And in having someone other than Apple or Apple Authorized Service Provide replace parts in your iPhone, Apple won't touch the phone now if you need service from Apple. This means you won't be able to trade the phone to Apple, and if you try to sell the phone to someone, you need to let them know the phone doesn't have an authentic Apple Battery in it, which will reduce any value the phone has.

Most of the time with a non-genuine battery, the Battery Health settings will not work correctly on your phone.

Settings > Battery > Battery Health & Charging > Maximum Capacity

If the correct setting for Maximum Capacity still appears, you are very lucky.