Modify a specific entry in fields

Step1 - Get the item in json format

bw get item <id>

can be stocked in variable or used directly with pipes

Step2 - Modify the entry

bw get item <id> | jq '.fields |= map(if .name == "token1" then .value = "new_value" else . end)' | bw encode

Step3 - Edit the entry

bw edit item <id> <encoded_json>

In one step

BW_ITEM_ID="<id>"
bw edit idem ${BW_ITEM_ID} $(bw get idem ${BW_ITEM_ID} | jq '.fields |= map(if .name == "token1" then .value = "new_value" else . end)' | bw encode)