Here's what you can do in Pokemon Diamond to help your Pokemon:
* Heal them at Pokemon Centers: Pokemon Centers are scattered throughout the region and allow you to heal your Pokemon for free.
* Use Potions and other healing items: You can buy various healing items at Pokemon Centers and department stores.
* Train your Pokemon: Battling and training your Pokemon will help them level up and become stronger.
* Use Vitamins: Vitamins are consumable items that increase specific stats, like Attack or Speed.
* Level up your Pokemon's friendship: You can increase your Pokemon's friendship by using items, winning battles, and walking around with them in your party. High friendship can sometimes help Pokemon learn new moves.
If you're looking for features like massages or proteins, they are more likely to be found in later Pokemon games like Pokemon Sword and Shield.