Hi @Anonymous,
Do you want to pass the File identifier from one flow to another flow using Microsoft Flow?
If you want to pass the File identifier from one flow to another flow using Microsoft Flow, I afraid that there is no way directly to achieve your needs in Microsoft Flow currently.
Passing variables from one flow to another flow directly is not supported in Microsoft Flow currently, if you would like this feature to be added in Microsoft Flow, please submit an idea to Flow Ideas Forum:
https://powerusers.microsoft.com/t5/Flow-Ideas/idb-p/FlowIdeas
In addition, you could consider take a try to store the File identifier into a SharePoint list and then add the "When an item is created" trigger as the trigger of your second flow (another flow). I created a SharePoint list on my side and the data structure of it as below:
Note: The File identifier column is a Single line of text type column, which is used to store the File identifier.
Please take a try with the follwing workaround:
First flow:
Second flow:
The flow works successfully as belwo:


Best regards,
Kris