how do i get my iphone 13 to charge when it says liquid detected but it is dry

Do not plug it in to charge when liquid is detected. If you charge your iPhone while the Lightning port is wet, the pins on the Lightning port or the cable can corrode and cause permanent damage or stop functioning, causing connectivity issues for your iPhone or accessory.

If your iPhone and Lightning accessory aren't wet

If you see this alert every time you connect a certain cable or accessory, that cable or accessory might be damaged. Contact the manufacturer.

If you see this alert every time you connect an Apple Lightning cable or accessory, contact Apple Support.

This advice copied from:

If you see a liquid-detection alert on your iPhone - Apple Support