Tenant wants deposit

[Estefania Lozano]

I recently purchased a new property. One of my tenants wants her $300 depot back, she had this lease agreement with the previous owner 25 years ago. He is in Thailand and she has no idea how to contact him. She also has no idea if she even has a copy of her lease agreement with him. I am letting her pay the same until the end of the years which is $450. She plans to move out at the end of the year but she mentioned she wants her deposit back. What do I do? I am new at this. Thank you!