does interaction with a magic neckless count as action in combet

I’m playing in Curse of Strahd model, and there is an item named holy symbol of ravenkind. This item hides behind the paladin character shirt. When the paladin have the sword and shield ready to battle and want to take out the HSOR necklace, does he need to sheathe or drop his sword before he can pull the necklace out? I tried to consult with this spellcasting in combat clarifications and restrictions article but it got me more confused. And if you need to sheathe the sword, does it take 2 action to draw it? example: 1st turn sheathe the sword 2nd turn pull the necklace and use it 3ed turn wear the necklace on the neck and draw the sword 4th turn attack with the sword this is how my DM said it should be, considering the necklace as an item like a sword.