So is there any way to reset my pet's hunger to 0/10 so I can feed more food. or do I have to just wait?

The Cleansing Pools at the Bathhouse in Shengui Guo. Choose Appetite renewal to reset hunger to 0. It can only be done once a day.

You can also use but it's a lot less certain. You have to use it in battle with the pet you are NOT trying to make hungry. When used, sometimes in battle it will give a message that a curse has been put on your other pets. This does things like changing hunger to 1/10, lowering happiness, lowering hp. However sometimes I can go through all 30 of my battle quests using it and not get the hunger curse a single time.

thank you!