JP1 Remotes

First of I'm pretty new to all this so maybe this is a silly question.
I uploaded Mag254.rmdu to my Atlas 1056B0 it basically works ok except for one key labelled "Back" on original Mag remote -the "Back" key on original remote gives/plays previous channel. On my Atlas no key gives me this function
Looking at Mag rmdu using RM no key is called "back" the closed is "return" however the return key does not give previous channel.
As a test I learned the "back" key from my original remote to my RCRP05BR and the learned key gives results as expected.
Hope I have made my problem clear
Thanx

If you learned the BACK button and it works, that should give you the OBC code, so you can add it to the RMDU file.

DVD Last 10 36036 RC5 14 15 C0 C1 C2 T=1
The above is the code-- OBC is 15 I will try editing locally but definitely not on original forum file!
Thanx

ok now I understand!
The original file is fine- "return" is the "last" key it just has to be remapped to the correct key