Stir hot water and tomato bouillon in a small bowl until dissolved.

Mix garlic powder, oregano, thyme, salt, and cayenne pepper together in a small bowl. Rub seasoning all over pork tenderloin until coated.

Turn on a multi-functional pressure cooker (such as Instant Pot®) and select Saute function. Add olive oil and heat until shimmering, 3 to 5 minutes. Add smashed garlic and cook until fragrant and oil is infused with garlic flavor, 1 to 2 minutes. Transfer garlic to a small bowl.

Add pork tenderloin to the pot and cook until browned, about 2 minutes per side. Pour tomato bouillon into the pot and bring to a boil while scraping any browned bits of pork off the bottom of the pan with a wooden spoon. Add garlic cloves back to the pot.

Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 0 minutes. Allow 10 to 15 minutes for pressure to build.

Release pressure using the natural-release method according to manufacturer's instructions, about 10 minutes. As soon as the pressure pin drops, unlock and remove the lid. Lift out tenderloin and cover with 2 layers of aluminum foil; allow to rest for 3 minutes before slicing. After resting, pork should be slightly pink in the center and an instant-read thermometer inserted into the center should read at least 145 degrees F (63 degrees C).

Meanwhile, mix cold water and cornstarch together in a small bowl to make a slurry. Add slurry to the Instant Pot®. Select Saute function and simmer until sauce has thickened, about 3 minutes. Drizzle sauce over sliced pork.