Open the Facebook app on your Android or iOS device. Select the three-line menu icon. Tap Settings & Privacy > Settings. Tap Personal Information > Contact Info > Add Email Address. Type your email address in the Add an additional email address box > Add email. Select Confirm. You will receive a text with the confirmation code. Tap the Enter confirmation code field. Most mobile devices will now display the confirmation code between quotation marks without you having to open the confirmation text. Tap the displayed code to automatically fill the Enter confirmation code box. Or, manually enter the code. Tap Confirm. This is how to change primary email on Facebook mobile or iPhone.