In your scenario, since you would like to update the same record's field, it is best for you to use the Fast Field Updates (as it is said to run typically faster; you can read about these 2 types here) and as cropredy suggested in the comment of your original post above, you can remove the starting condition.
When you remove the starting condition, the flow will automatically run, every single time you create or update the record.
But I would personally advice you to make sure to update the value, only when the Recurring_Revenue__c field value changes or it is a new record. If not, you would be updating the record every single time for no reason.
So, remove the starting condition.
- Put a decision element, and name the first outcome as New Record/ARR Changed and leave the default outcome as it is. (You can name them whatever you find it easy for you to understand).
- For your New Record/ARR Changed branch, you can put the condition where, Record.Id does not equal RecordPrior.Id, which means the record is new. Because, as you can imagine, if you are updating a record, the record will have a prior Id right? + OR Condition it with + Record.Recurring_Revenue__c is changed True.
These condition means, if the record is new or if the record's Recurring_Revenue__c field is changed, then the flow will traverse/take/follow this path/branch.
The image below, is just an example
- Finally add your update record element under this branch.
In summary, this flow will run everytime you create/update record (of the object you specified in your starting condition). Then it will check if the Record is new OR Record's Recurring_Revenue__c is changed. If it is, then you can copy the field value using the update record element. If any of these conditions is not met, then the flow will follow the default outcome path and end (meaning it doesn't do anything).
I hope this help you to understand flow better. If you need more explanation on certain things I have mentioned above, please add a comment I will be more than happy to edit the post again to add more information!