thanks for your advice but I know English & Bengali, which I am interested to teach for free

Taking without giving doesn't work here. Everyone is busy achieving their own goals; being a teacher takes a lot of time and effort. Give people a motivation to spend their time and efforts helping you. At least, show them that you do work on language hard, and they will help you.

I do not understand what did you say

А как же? Вот только тапки зашнурую... :D