What can I provide if I do not have a National ID card?
A copy of the birth certificate — the document lists both as alternatives.
In detail
The requirement reads “A copy of National ID Card OR Birth Certificate (whichever applicable)” — one or the other, whichever fits your case. For applicants under 18 who do not yet have a National ID, the birth certificate is the natural choice.
What matters most on this document is not the number but the spelling of your name. It must match the passport exactly. Small differences in the romanisation of a Bengali name — Mohammad versus Mohammod, or Rahman versus Rahaman — are very common, because the documents were issued at different times by different offices.
Put the passport and the ID side by side and compare them letter by letter before you apply.