One of those blacks will be a switch wire basically a live (should be a red) and the other will be the N
The red on its own is likely the permanent live (not switched)
To find which black is N (you will need test lamps to do this) make sure the switch is on and test across each black and earth, you should get 230v reading when you test across the switch live and earth
(if you test across N & earth you won't get 230v showing)
Once you know which black is the switch wire you connect the brown on your fitting to this
Then you connect the blue on the fitting to the other black
The earth to the earth
And there should be nothing to connect to the reds
Good luck
