It should be possible by deleting the old trigger action and selecting and configuring the new one. See the animated gif below as an example.
Only thing you might need to do is update other actions as well (expressions or dynamic content fields which were used from the original trigger action).
You could use an trigger condition expression to check if the System_ChangedDate is equal to the Microsoft_VSTS_Common_StateChangeDate.
Below is an example
I have tested this with a Bug work item for the Scrum process btw. I do not know if this would work with other process. You might need to use other fields.
I've already tried many options, but nothing works...
Now I will explain how my flows work: I am create initiative and Flow 1 is running, in my process i am configure State, its like New 1, New 2, New 3 etc... I want when i change State from New to New 1, Flow 2 need run. How i can do this ?
You can only check if the State field has changed and to which value it has changed. You cannot check what the original value was in a trigger condition.
Assuming you are using the Scrum process with a bug work item and you are using the out of the box System_State field you could use the following expression:
@and(equals(triggerOutputs()?['body/fields/System_ChangedDate'],triggerOutputs()?['body/fields/Microsoft_VSTS_Common_StateChangeDate']), equals(triggerOutputs()?['body/fields/System_State'], 'New1'))