screen problems after trying waterproof test

For what Apple states ➡️ About splash, water, and dust resistance of iPhone 7 and later - Apple Support

Which includes the following:

To prevent liquid damage, avoid these:

• Swimming or bathing with your iPhone
• Exposing your iPhone to pressurized water or high velocity water, such as when showering, water skiing, wake boarding, surfing, jet skiing, and so on
• Using your iPhone in a sauna or steam room
• Intentionally submerging your iPhone in water
• …

Above-linked article also includes drying instructions, though damage can be permanent, and won’t be covered by the standard warranty. AppleCare+ coverage might cover this, though there’ll be a fee if so.

Sorry? "waterproof test"?

Are you saying you intentionally submerged the phone?

Congratulations, you have voided the warranty and pretty much guaranteed that the phone will fail completely in short order.

It is NOT waterproof. It is water resistant. There is a huge difference.

You will have to pay for a replacement.