Request Vietnamese govt release Mr Thanh Do who was caught for having different political viewpoint; US gives him asylum

I am writing this letter with regards to my father's case (Mr. Thanh Do). He immigrated illegally to Cambodia from Vietnam and tended to flight to Thailand to connect to the UK for REFUGEE (for having different political viewpoint - Attachment) on the 13th July. However, he was caught in Phnom Penh airport due to illegal immigrant. For the last time contacted, he was kept in the immigration office or something for investigation. He texted me in Vietnamese so I guess he was either in the Immigration Department or the General Department of Immigration. I was told that he would claim resettlement refugee programme to come over, then they disappeared. He is also with his wife (Hien Dinh) and his daughter (Yen Do, who is under18). There is no reason why my mom and sister are kept their as well