iOS devices do not have a built-in NFC writer function. This means that you cannot use your iPhone or iPad to write information to an NFC tag. However, you can use third-party NFC writing apps that are available on the App Store.

Here's how you can use an iOS iphone NFC writer app:

1. Download an NFC writing app from the App Store. Some popular options include NFC Tools, TagWriter, and NFC for iPhone.

2. Open the app and follow the instructions to create a new NFC tag or write data to an existing tag.

3. Once you have written the desired data or information to the tag, you can use your iPhone or iPad to scan the tag using the built-in NFC reader.

4. If the tag's data is compatible with the associated app or action, your iPhone will display a notification and prompt you to take the appropriate action.

5. If the tag's data is not compatible with any app or action on your iPhone, you may need to use a different device or app to read and interact with it.

It's important to note that not all NFC tags are compatible with iOS devices. Make sure to choose an NFC tag that supports NDEF (NFC Data Exchange Format), which is the data format used by iOS devices. Also, different NFC writing apps may have different features and capabilities, so it's worth trying out a few different options to find one that meets your needs.