Resetting Littlest Pet Shop Digital Pet help

I have three littlest pet shop digital pets that I bought used. They are the version 2 type, with the two hanging charms that you use to care for your pet. I only have batteries in one of them right now. I want to reset it to erase all the sticker and stamp progress from the previous owner. I'm doing what the instruction manual (looked it up online) says, which is to hold the two front buttons and press the reset button on the back using a pen or paperclip. And it's not working. How long do I need to hold the buttons down for? Every time that I try to reset, I go back and look at the diary and all the stamps and stickers are still there. Help!

Well from the instructions you explained, that would be the way to do it.

Should I maybe try taking it apart and cleaning around the reset button?

Weird, the two I have reset fine when I held the buttons while resetting. If I remember correctly, they went into the "try me" mode that they had while in stores. Only problem was the instructions I got said to just press the reset button, which isn't how to do it. Note: I do not know which ones I have exactly, I just know one is a cat and one is a butterfly and I'm supposed to find pets that escaped.