You need to create a variable (vector), and set it when the OnSeePawn event is triggered. The value will be the world location of the pawn that the event transmits.
In the Move node, you need to connect a variable with location, and break the reference to the character.
As a result, while the zombie sees the player, the location will be constantly updated, and he will go to the player.
When the player hides, the OnSeePawn event will stop being called, and the zombie will go to the place where he last saw the player.