Assistance with solid Boolean for printing

[L i am]

Hi all, have have my first 3d printing project which is a bit of an emergency (like really) Box has been very kind in assisting me with the model for printing. But Box is in Sydney and would be asleep now. I tried to make a required technical change but due to my ignorance of 3 d printing received a note from the printer guy saying my efforts to modify Boxes model have stuffed it up
Could somebody please make "A" look like "B" for me to convert to an STL? I did the "Boolean" by intersect faces, but another way is required it seems. Assistance would greatly appreciated.

[Box]

I'm awake but unable to help as I'm only on my phone.

[L i am]

Understood, thanks mate

[Box]

Had a quick look and I'm not sure what you have done, but it is after 3am now. I think you need to tell me what it was you tried to change and perhaps I can edit the original.
Or if you are still awake upload the original and explain what you need and someone on the otherside of the world may fix it for you while you sleep.

[L i am]

Thanks Box, you must be an owl. I awoke to find the printer guy fixed it with a program that "fixes" geometry.