Here are the most common methods (note: these guides are for educational purposes and should be used cautiously):
While there is no official "free" iOS version of Hollow Knight from developer Team Cherry
Will you be playing with or a Bluetooth controller ?
When searching for a free Hollow Knight IPA, exercising caution is vital. Downloading files from untrusted sources puts your device and personal data at risk.
Would you like recommendations for legitimate mobile Metroidvania games instead?