Yeah, 5e rules do not allow Eldritch Knights to use spell books. They can change one of the spells they know when levelling up. They are also supposed to be mostly limited to Abjuration and Evocation spells.
What they can do is multiclass to wizard. 1/3 of your EK levels (rounded down) stack with your wizard levels for determining your spell slots, and you can use those slots to cast either the spells you know as an EK or the spells you know as a wizard.
Last edited by FrostyFardragon; 07/11/20 12:27 PM.