Apple iPhone 8 font too big. Unable to use passcode.

You may need to vary the speed and timing of the double-tap to nail it.

If still no luck, try a Forced Restart on the phone. Follow the instructions very carefully, as this is a bit tricky. (Hint.....ignore the "slider" when it appears and keep holding the Side button in until the Apple logo appears. This might take another 30 seconds.)

Force restart iPhone - Apple Support

Vamboop wrote:

1. I tried both but did not work. I went on Google and found other option to restart phone.

1. press increase volume and release quickly

2. Press decrease volume release quickly.

Hold the side button until the Apple display. Then phone restarts. The font returned to normal size afterwards.

Which is EXACTLY the procedure detailed in the link I provided.

I tried both but did not work. I went on Google and found other option to restart phone.

1. press increase volume and release quickly

2. Press decrease volume release quickly.

1. Hold the side button until the Apple display. Then phone restarts. The font returned to normal size afterwards.

Somehow, you must have missed the two answers that told you do this, so you could have saved yourself some time. But, glad that your issue is resolved.

Did you put three fingers together, holding them together and tapping your iPhone screen TWICE with a bit of force in rapid succession?

If that doesn't work, Force Restart your iPhone --> Force restart iPhone - Apple Support (CA)

You're welcome.