I can’t pair my Apple Watch with my new iPhone

If your iPhone was previously paired with another iPhone, you’ll need to unpair it. Then, you may pair with watch with your new iPhone. From your watch, you can also select ‘Settings,’ ‘General,’ ‘Reset,’ then ‘Erase All Content and Settings.’ Your Apple Watch will reset, allowing you to pair it with a new iPhone. Be aware, however, that you’ll be prompted to enter the Apple ID and/or the passcode for the Apple Watch during this process. For security reasons and to prevent theft and misuse, Apple links devices to iCloud accounts in such a way that they can’t be set up with a new iCloud account until the link to the previous account is removed. I hope this answers your question. Good luck!

If your question is about updating your Apple Watch Series 3, you will be limited on space for updating it. However, it is still possible and I’ve been able to do so by following guidance from Apple. Here’s a link to the Apple support page to assist you with the installation of updates on Apple Watch. I hope this is helpful. Good luck!

https://support.apple.com/en-us/HT211283

I haven't got a question,my reply was to the op.