If you want to change your Dispatch / Airstrip password, you can do so by:
Going to Dispatch
Clicking on your avatar in the top right corner
Selecting "Profile Settings"
As such:
Note: your password has to be longer than 10 characters! If you cannot think of a good password or keep forgetting them, consider using a password manager like 1password (OSX / iOS now has a native password manager as well).