Under the finance law – 2015, those who have a yearly income of more than 2,50,000 BDT are considered eligible to pay tax. This includes non-resident Bangladeshis, Hindu Joint Family, Partnership firm, Association of persons. But

1. Females & Elders are aged 65 or more taxpayers' income is above 3,00,000 BDT.
2. Physically challenged taxpayers' income is above 3,00,000 BDT.
3. War wounded gadget enlisted freedom-fighter taxpayers' income is above 4,25,000 BDT.

You have to visit https://incometax.gov.bd/TINHome. Then register yourself for the site and apply for the e-TIN providing required info like Name, Address, NID number, etc. Note you can have only one e-TIN registration.