Recently The government of Bangladesh has restricted some social apps in Bangladesh due to security issues.
From pc just installed Tor browser and browse Facebook from this browser as like other browsers.
From mobile if you have smart phone then use Hola apps. And connected with Facebook with uc browser.
In mobile phone which is normally called not smartphone can be use Orweb private web browser.
In mobile devices it's bit difficult to use Facebook in Bangladesh because you have to know how to configure it properly. But for pc users you can easily browse Facebook just using tor or any vpn software.