you can change the id to a string. In the flow you can make a variable. For example TempID (type = string).
Now you can start with your database retrieve: [id=$TempdID]
An second option (when you know the right ID): give your microflow a parameter (name = ID). After that you can create a variable (string) and convert the autonumber to string.
Why would you need the internal id. In a microflow if you have the other side of the association you can say: [Entity.AssociationAB=$your-object] or [Entity.AssociationAB/OtherEntity/id=$your-object]
If you have another unique identifer you could say [AutoNumberAttribute=value]