The sensor is trickey. Ull need AC to get reliable readings.
U can use two digital outputs to make ca. 1kHz sq.wave. Use a serial 50k..100k resistor to make a voltage divider. After cycling AC for a couple of secs. Read the analog voltage.
The datasheet can help you with info to calculate RH
When you see that it is very temperature dependent, you may want to use something like DHT22..