I think what you are probably trying to find out, is precisely why he got his OBE. That can be extremely difficult. The recipient often doesn’t know the exact reasons. (I know from personal experience).
The person who recommends you for an award writes up the reasons confidentially and sends them to No 10 or the Cabinet Office. If approved, your name goes forward to the King or Queen and you may later get offered an award. However at no time in the process are you formally given a copy of the reasons or of the citation. The person who recommended you may tell you, but otherwise you remain in mildly confused ignorance. Any citation in a newspaper usually gives a most general description. For example in your ancestor’s case, it may just say “For public service in Nigeria”, or “services to Lagos Town Council”. As an example, Paul McCartney was made a knight in 1997. I know nothing of the details but I expect it was reported publicly along the lines of “services to the music industry.” That’s about as far as you will ever get with these things.
The original citations must be filed away somewhere but they don’t appear to be in TNA in Kew or any other public repository.