dogogo Guardian Trident Dog Light, Green

This is a great light but I bought it on 11th December and by 5th January the battery had run out. To make it worse, I've mislaid the instructions and for the life of me cannot find how to replace the battery. I checked the Amazon web site to try and contact Doggo, the supplier, and there is no 'Contact supplier' option on the site. Where do I go from here? (I'd have given it five stars for the light it gives but replacing the battery in less than a month is not an option).

I am extremely disappointed with this product. It was a pain trying g to open it and then after having to use force to complete this exercise; we couldn’t turn it on after I setting the batteries. I would not recommend buying this item.