I want to know how to get historical record of my country sachable online
Custodians of historical records are in control. The FamilySearch Research Wiki pages for Nigeria include some contacts.0
You might try contacting representatives of your country/government/record holders
and see if they might be willing to work something out with FamilySearch to digitize their records.
Its quite possible there may not even be costs - though I don't know for sure.
once you get some contacts we can help put them in contact with the right people here at FamilySearch.
for the most part as said - it is up to the country in question - to give permission to index/digitize such records.0
Note that alot of Nigerian records are coming from the FINDAGRAVE project
Have you ever worked with Findgrave?
You might find some satisfaction in being involved in the Findagrave Project for graves/buiral locations in Nigeria and other parts of Africa.
I have also been involved with Findagrave -- it doesn't always mean that you have to visit some cemetery in Nigeria -- there are numerous ways to get involved.
and such records -- then flow into FamilySearch