To do so on iOS, head over to your profile, tap on the gear icon in the top right corner. In settings, you'll find either "Verify email" or "Change email". Both flows will allow you to change your email address.
In addition, you can only change your e-mail address if you have created an account for InVintory using and email address (and password).
If you have signed in by your Apple ID or through your Google account, you would have to contact Apple or Google to change the email that you associate with those accounts.
On the web app (see app.invintorywines.com), first click on your profile icon in the top left corner. Once the page opens, you can see a field for e-mail address which you can change and then select the gold update button in the bottom right corner.
If you can’t find your login e-mail, you can select to Contact Us and firstname.lastname@example.org