wires disconnected in back of dryer
a yellow box called d.e.m f3cc73002v5


That would be an interference suppressor. It has a useful circuit diagram on it which shows how it should be connected. It also shows what it contains (three capacitors and a bleed resistor)

Some images from eBay:



L is the live wire in brown insulation
N is the neutral wire in blue insulation
The terminals at the top of the picture are for the earth wire in green/yellow striped insulation.

Note that the middle brown wire has a plastic insulating shroud to keep it apart from the blue wire. That protection is important.

However if all these have been ripped out by force there may be damage that needs repair.

All the connectors on this device are male spade connectors. The wires that connect to them should have female spade connectors crimped onto them. If they have been pulled forcefully off, they are likely to be damaged - check that there are no broken strands. 

A damaged wire or connection could start a fire.

A loose wire, could blow a fuse or trip a breaker or electrocute anyone touching the dryer.

The safest thing to do is to get a service engineer to check and fix it.