Thx Ray, it works for me. What about to add a new label in second position or third etc ... I have to add more than one label on different condition. I used automated actions using your python expression but each label erase the one before :-(

Edit on 09/05/2022
To add a new tagg, you have to use : [(4,443)] 

on documentation you can read this :

(0, 0,  { values })    link to a new record that needs to be created with the given values dictionary
(1, ID, { values })    update the linked record with id = ID (write *values* on it)
(2, ID)                remove and delete the linked record with id = ID (calls unlink on ID, that will delete the object completely, and the link to it as well)
(3, ID)                cut the link to the linked record with id = ID (delete the relationship between the two objects but does not delete the target object itself)
(4, ID)                link to existing record with id = ID (adds a relationship)
(5)                    unlink all (like using (3,ID) for all linked records)
(6, 0, [IDs])          replace the list of linked IDs (like using (5) then (4,ID) for each ID in the list of IDs)

6 is option to replace a record, 4 is the opption to update :-)

Thanks Robocath, this help me a lot, I am creating check box for to Sales man just click and a tag being created automatically on contact tags, with your explanation works like a charm, just the only thing I need is if the box is uncheck that the tag also be removed, any help here please!!