owningCharacters = [object1, object2, object3]

My DB has an array and it has multiple objects.

owningCharacters [Array]

0: Objects {}

1: Objects {}

2: Objects {}

I edited an object's value and saved it like this.

owningCharacters[0].level++;
for(let i = 0; i < user.owningCharacters.length ; i++){
   user.markModified("owningCharacters");
};
user.save();

but DB didn't save the edited value. So I also tried like this too.

for(let i = 0; i < user.owningCharacters.length ; i++){
   user.markModified("owningCharacters." + i);
};
user.save();

for(let i = 0; i < user.owningCharacters.length ; i++){
   user.markModified(i);
};
user.save();

And these tries didn't work either.

How can I save every single objects in an Array?