How many UR points do you have?

There aren't really any secrets about it these days. You have two possible paths:

1. Use the UR points to book flights via Chase. For points earned before last October when they revamped the program, you get $0.015 per point. For points earned afterwards, you get a variable amount between $0.01 and either $0.015 or $0.02 (I forget). This is assuming you have a Sapphire Reserve. For the CSP I'm not sure what the valuation is.
2. Transfer the points to an airline and book a miles award ticket. Delta isn't a transfer partner, but KLM/Air France are so if you wanted to fly Delta you could transfer to those programs and book a codeshare. United is a direct transfer partner, so you could book via United and also use your 250k miles. You'll be hard pressed to find saver business awards to Europe in September (still kind of high season) but you might get lucky especially closer in, like a month or a few weeks out. And I think United is moving to a dynamic award pricing model anyway.

You can sign up for a seats.aero membership and set alerts for saver business availability on the routes and dates you want (or flexible dates). When it alerts you, log in, transfer the points, and book. You can also sign up for upgrade availability alerts. Don't transfer points to an airline until you know there's availability, since you can't transfer them away from airlines generally. Transfers are usually immediate, but sometimes they can take a few days.

If you book with United, you can also go to Advanced search and search manually for upgrade availability. If you get lucky and book such a flight, you can request an upgrade with miles at booking and it will immediately confirm with no waitlist.

You can probably get business if you're willing to be flexible with dates and/or book closer in.