I cant install the ios 17.3 in my iphone 11 pro max. Can you help me to fix this? Thank you

A clue might be that the screen says it is "Installing" but things may be hung up because the servers are overloaded with millions of folks trying to update at the same time.

Unfortunately, there is no quick easy fix. You will have to work your way through Apple's troubleshooting guide for updates:

If your iPhone or iPad won't update - Apple SupportApple SupportOfficial Apple Support › en-us

I do not know the answer because there are a number of different possibilities for the problem. But if I had the same problem I would carefully follow the steps in the document that I posted.

If your iPhone or iPad won't update - Apple SupportApple Support

What happens when you try? What exact error message appears?

A screenshot would be really helpful here.