You can change your account password on your Airtable account page. To access your account information, click the circular face icon in the top right of the home screen. This will bring up a dropdown menu with several options; select the option "Account" (which has a little silhouette of head next to it).
This will bring you to the "Your Account" page. If you click the blue words that say "Change Password," a dialog will appear allowing you to choose a new password.