How can I trigger a flow action only once while updating contact?

How can I trigger a flow action only once while updating contact?

Hi,
we have a trigger to merge&mail file when the field YYY is filled out. For this acion I used "Create or update module entry".
But unfortunately we get tens of email on a day with this merged file, because the contact is being regularly updated. The merge&mail action should trigger only once!

I have read all the posts about this problem but I cant find a solution for our problem. Can anyone help me please??
Kind regards,
Victoria




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