Scrolling the terminal is possible, just swipe up and down anywhere in the main view. For scrolling your history, use the arrow key in the custom keyboard addition.

If you hide the keyboard, you can make it re-appear by tapping anywhere on the screen.

iSH comes with a custom keyboard addition.
At the top of the keyboard you'll find an extra set of keys. It helps with navigating in the terminal, and contains useful modifier keys.

Here's what they do:

Navigating with the arrow key is simple! Press the key and slide your finger in the direction you want. The key will repeat.

On iOS versions earlier than 13, pressing the (i) in the extra row of keys will bring you to the settings page. In iOS 13 or later, the button is a cog instead.
From here you can quickly set a theme, re-map keys, or disable screen dimming.

There is also a button to quickly send email feedback. Links to iSH on other websites are also located here.