After a while of being turned off it reverts to normal.

Here are the steps I take to set TX Offset

1) Set the step to 12.5
2) Set the RX frequency
3) Set the CTCSS for RX / TX e.g. 118.8
4) Press and hold (left button |) until '+ -' flashes
5) Enter the TX frequency
6) Press the light / transfer button

However after step 4 I cannot enter a frequency
Please help, I took the steps from the AP73 manual