Many thanks for the link.
The evtest shows
hpprol2:~ # evtest
No device specified, trying to scan all of /dev/input/event*
Available devices:
/dev/input/event0: Power Button
/dev/input/event1: CHICONY HP Basic USB Keyboard
/dev/input/event2: Kingsis Peripherals Evoluent VerticalMouse 4
/dev/input/event3: PC Speaker
Select the device event number [0-3]: 2
Input driver version is 1.0.1
Input device ID: bus 0x3 vendor 0x1a7c product 0x191 version 0x111
Input device name: "Kingsis Peripherals Evoluent VerticalMouse 4"
Supported events:
Event type 0 (EV_SYN)
Event type 1 (EV_KEY)
Event code 272 (BTN_LEFT)
Event code 273 (BTN_RIGHT)
Event code 274 (BTN_MIDDLE)
Event code 275 (BTN_SIDE)
Event code 276 (BTN_EXTRA)
Event code 277 (BTN_FORWARD)
Event type 2 (EV_REL)
Event code 0 (REL_X)
Event code 1 (REL_Y)
Event code 6 (REL_HWHEEL)
Event code 8 (REL_WHEEL)
Event code 11 (REL_WHEEL_HI_RES)
Event code 12 (REL_HWHEEL_HI_RES)
Event type 4 (EV_MSC)
Event code 4 (MSC_SCAN)
Properties:
Testing ... (interrupt to exit)
Event: time 1709215636.116517, type 4 (EV_MSC), code 4 (MSC_SCAN), value 90003
Event: time 1709215636.116517, type 1 (EV_KEY), code 274 (BTN_MIDDLE), value 1
Event: time 1709215636.116517, -------------- SYN_REPORT ------------
Event: time 1709215636.293512, type 4 (EV_MSC), code 4 (MSC_SCAN), value 90003
Event: time 1709215636.293512, type 1 (EV_KEY), code 274 (BTN_MIDDLE), value 0
Event: time 1709215636.293512, -------------- SYN_REPORT ------------
Event: time 1709215637.468573, type 4 (EV_MSC), code 4 (MSC_SCAN), value 90002
Event: time 1709215637.468573, type 1 (EV_KEY), code 273 (BTN_RIGHT), value 1
Event: time 1709215637.468573, -------------- SYN_REPORT ------------
Event: time 1709215637.601500, type 4 (EV_MSC), code 4 (MSC_SCAN), value 90002
Event: time 1709215637.601500, type 1 (EV_KEY), code 273 (BTN_RIGHT), value 0
I created the directory /etc/udev/hwdb.d and therein the file 99-test.hwdb with this content
evdev:input:b0003v1A7Cp0191*
KEYBOARD_KEY_90002=btn_middle
KEYBOARD_KEY_90003=btn_right
therafter
# systemd-hwdb update
# udevadm trigger
and the button are swapped 
I removed the evmouse.sh script
Mant thanks for your help
Philippe