Hi there, you have activated the 1.7 Beta version in which Page Header has been deprecated. It now resides in Appearance > Elements > New > Header – Page Hero.
Tom shows it off here:
https://generatepress.com/gp-premium-1-7/
Although current tests have proven it is very stable, and the live release is expected soon you may want to roll back to the previous 1.6.3 version. You can do this by deleting the plugin, downloading the zip file from you GP Account, and re-installing. Look for where you add your license key (on the page your screenshot is of) and uncheck the Receive Beta Updates.