How do I wire a 3 wire receiver unit to a ceiling fan that has 6 wires from the fan unit
Are you in Europe?  Blue means neutral there.  America doesn't use blue, neutral is white or gray. 

One of those wires must be "hot" for the lamp. 

All the other wires are speed control of the fan.  By connecting, isolating or cross connecting various wires, you get various speeds.  The old switch knows how to do that. 

The new receiver does not.  It expects to only switch the fan on/off and "something downstream" manages speed, e.g. with a pull cord.  If you want that functionality, you either need a receiver that supports all those wires, or find a way to move or add the proper speed selector switch to the fan proper. 

You might be able to retain the old speed selector switch, and have it takes its power from the receiver instead of from always-hot.  Then the receiver would control off/on, and the old switch would control speed.  That may mean putting the receiver next to the old controller instead of up at the fan.  Identify the lamp wire, and bypass that on the old switch and let the receiver control it directly.  However there's a risk to that: most fan control switches force you to start the fan in "high".  That's because if you start in "low", it may not have enough torque to start turning, and sit there stalled overheating the windings. It's best to use only products listed/rated for that purpose.