The 857D does not support "banks" as we usually think of them.
It supports memory grouping. It just partitions the memories into 20 memory segments. On = scan 20 memory segments. Off = scan all 200.
You cannot assign a memory to a bank.
From the manual...
MENU MODE No•055 [ MEM GROUP ]
Function: Enables/disables the memory grouping feature.
Available Values: OFF/ON
Default: OFF
When this Menu Item is set to “ON,” the 200 “standard” memory channels are partitioned
into ten Memory Groups, each holding up to 20 memory channels (the Group size is fixed).
There isn't a setting to assign a channel to a bank which is probably why Chirp doesn't have that option available for the 857D.
There is a Quick Memory Bank (QMB) feature where you can "bank" a channel of interest that is mentioned but I never used it.