what are the procedures to get the visa for bangladeshi national for China and Hongkong

For China visa, they can submit the visa requirements to China embassy in Bangladesh. The officers will then process the visa for you. Here is a list of visa requirements by China embassy in Bangladesh: https://www.travelchinaguide.com/embassy/bangladesh.htm
For Hong Kong visa, they can also submit the requirements to china embssy in that country to have the visa processed or post them directly to hong Kong Immigration Department to apply for the visa. Here is Hong Kong visa requirements: http://www.immd.gov.hk/ehtml/hkvisas.htm