Question on Puxing 777

Hi. I am new to the world of two way radios. I just bought my first two way radio, a Puxing 777. The user manual says the frequency range is 136-174Mhz and 400-470Mhz, but every time I key in any frequency between 136-174Mhz the display goes back to the default frequency of 400Mhz. All frequencies between 400-470Mhz work fine.
Anyone here know how I can change the frequency range on the Puxing 777. Any help would be greatly appreciated.

er, you’ve bought the UHF version then, NOT the VHF one - they are NOT dual band, just available to buy in both. That’s probably not what you wanted to hear?