How to claim deceased bank account

Hello po! I hope someone can help me for guidance on how to claim deceased atm account of my mother. Problem po is nawala na yung ATM nya, and more than 2 years na syang in rest in peace. Nalaman lang namin na meron pa syang around 6k sa banko when nagpadala ng notice sa amin na dormant na yung account nya and needs to re activate. kaso nga po passed away na sya, ano po ba requirements and kung malaki po ba magagastos kasi 6k lang nman and natira at baka may penalty pa sya bayaran sa bank. Di ko rin po sure kung nakalagay ako as beneficiary sa account wala din naman po last will. Hoping na may magadvice, thank you po!