How to add spells to an existing monster?

[Owlbear]

I am preparing Curse of Strahd and I tried to make a portfolio for Sir Godfrey Gwilym, a revenant who is also a 16th level paladin.
I started from a standard revenant to get all the special abilities.

I know I can add paladin levels to get the spellcasting ability, but that adds a lot of unwanted abilities, hp, prof bonus, etc...
So I used an adjustment to add each spell manually as a racial spell. The problem is that there is no (racial) spell tab if I do so and I cannot choose the spells as prepared. Am I missing something?
Please note that I am a quite new user and I do not know how to use the editor.

Thanks in advance.