You'll need to locate and extract the unit that is BM54 so it can be taken or sent to a repair website.
The real BMW BM54 repair is generally so simple the unit could be returned to you personally on the same day it's received, or done in a couple of hours (if you take it in to your repair centre yourself) to be picked up on the day you drop it in.
The BMW B54 radio unit is manufactured by an organization called Becker, whose high class sound has been keeping BMW and Range Rover owners (among others happy for many years. You will find a BM54 unit in the BMW 3 series the BMW X5; and some Land and Range Rover models. Your owner's manual should inform you what version of unit that is BM54 you've got in your own car.
The BMW BM54 repair begins with fault identification - so you need to inform your engineer what is wrong with the unit. Common faults in the BM54 contain loss of sound to one or more channels; total loss of sound; or only some of the speakers working. Be aware that just the speakers in a single area of your vehicle are faulty, or if one of your loudspeakers is not faultless, it might not be the BM54 unit at fault but wiring inside the doors.
You could have your BM54 unit assessed for faults in situ before you send it away for the BMW BM54 repair. It's best to do this because otherwise you won't know for sure that it is the unit itself causing the issue. And obviously if that unit is sent by you away without a problem,, it will come back not needing fixing and you'll still have that issue - plus you will have needed to pay the BMW BM54 repair centre for the time.
If you're unsure where to get a BM54 assessed before repair, you are able to ask the center to which you are sending it to do a complete BMW diagnostic check on it before they start to repair it.
Every BM54 unit is located under the spare tyre - normally in the boot well, in an area that was somewhat different. For instructions BECM Repair on removing the unit that is BM54 prior to the BMW BM54 repair, refer to blogs or have a look in the manual of your manufacturer. In case you have some questions contact the business that is going to do your diagnosis and repair and request their advice.