`docker service update` not working to update config - docker

Question

Firstly every step is done seemingly successfully (not any error reported). But per what I understand about how to check if the new config is applied OK, it seems to be failed updating the config.
Suppose I have a config file with a simple content like this:
Well done
I created a config (the first version) like this:
echo 'Well done' | docker config create my-config -
Now I have a local file named my-config.txt (on the host machine) with content as described above, it's used as a template (source) to clone over the target on the Docker container. On the Docker container, there is already a config file with the same content (originally). Now I change the content of the file my-config.txt (on the host machine) to something like this:
Well done !!!
And next I update the current docker service (created before) by using docker service update to apply the new config file, like this:
//firstly create another version of config
docker config create my-config-2 /home/my_user/my-config.txt
docker service update \
--config-add source=my-config-2,target=my-config.txt \
--config-rm my-config \
my-service
As I said, it seems to execute successfully. But when I try opening the my-config.txt file on the Docker container, its content is kept unchanged, like this:
docker exec [container_id] cat my-config.txt
It still shows Well done whereas the expected content should be Well done !!!. Isn't that what it should be? Am I doing something wrong here? Or could you suggest something to diagnose this issue or something different from what I've done without having to trying to solve this issue?