From the table WCDMA 850 is 26 so you need to shift 1 across 26 bits which in binary would be
100000000000000000000000000 which is
4000000 in the hexadecimal notation that command requires, so it should be:
I've left the leading zeroes in place as shown in a datasheet example, I'm not sure if they'd be required or not. If you're a Windows user you can use the calculator to do the same conversion by selecting View | Programmer mode, entering 1 followed by a press of the "Lsh" (left-shift) button and then 26 followed by the "=" button. Then press the Hex button to get the result in hexadecimal.
As you've found that the module is not working with that bit set to work back from an example of the
AT+CNBP? where you received the result
0x000700000FFF0380 if I paste that into the Windows calculator while Hex mode is selected and then press the Bin (Binary) button I get the following result:
This result has 51 binary digits (numbering starts at zero) and reading from right (which is bit zero) to left (which is bit 50) you can see that WCDMA 850 is enabled. However that's not a guarantee that the module variant you have actually supports it and if it doesn't it may not like that bit being the only one selected. It may be worth trying to replace some of the selected bits to confirm it. For example if you know GSM 850 is currently being used perhaps try the following:
Which back in hex with the leading zeroes is
0x0000000004080000. If you're unsure which network is currently being used the
AT+CPSI? command provides that.