Playing Curse of Strahd as an arcane trickster rogue - after temporarily dying, I came back to life and DM said I gained access to Shadow Blade (warlock/wizard spell). To add this I copied the description of original and made a homebrew spell of it. It is in my collections along with being in my creations. I set it so its for arcane trickster rogues. However when I have lookedd to add the spell, its not appearing as an option. I have enabled homebrew content on character editor.

I created the spell yesterday on a different device and still not working. I have tried levelling and de-levelling my character but it is still not appearing as an option.

Arcane Trickster Rogues use spells from the Wizard spell list. Shadow Blade is already a Wizard spell. Arcane Trickster rogues already have access to it. There was no need to make a homebrew copy.

The "available for classes" box should never ever, ever, ever be used for subclasses you did not homebrew. It is a majorly temperamental and poorly made thing and can cause some fluffups.  

If the DM meant you can now use the spell outside of your normal spell selections when levelling, you will need to make a homebrew copy of the subclass and add a subclass feature that adds it. Or just make a custom action on your sheet for the attack and damage rolls and mark off your spell slots manually.

I've worked out the issue, it's because I am currently level 6 and arcane tricksters access 2nd level wizard spells from level 7! Thanks for your reply and guidance though.

Quote from SamBR2303 >>

I've worked out the issue, it's because I am currently level 6 and arcane tricksters access 2nd level wizard spells from level 7! Thanks for your reply and guidance though.

 
Oh for something like that then make a magic item with 1 charge and assign the spell to use that 1 charge.