If you don’t find a smooth workflow to do manually and want an automated solution, you can use Order Automator to handle jobs like this.
For your use case, here’s how you would do this in the app:
Create an Auto Tag rule to Tag Customers with SOME TAG if the order tag contains SOME ORDER TAG (ex: SS25)
This would now start checking new orders and apply the tag to the Customer, if the order conditions match
To bulk process orders already in your store, go to the Batch Process page and select a date range to process those orders from your campaign
There’s a 7 day free trial with the app, so if you’re tight on budget and just need this 1-time job done, you can use the app for that then uninstall it within 7 days (but check out the other features first, you will probably find something useful to help you out :D).