What are the markings on the old switch?
What are the symptoms of the problem?
Could be you need to join the two blacks together in a spare piece of terminal block if they are neutrals.
One red to Com
The other red to L1.
get them to take the cover off the light itself and take a photo and post it on here, also the connections in the fan and it's isolator, and of the wires dangling out of the ceiling.
Nothing we can do. The old switch may have been a double pole switch, or it could be that the two blacks need to be connected together. A multimeter would be handy. Failing that, a qualified spark.
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