There is no "return connects for a refund" button.
And you don't actually need to cancel your account. How would doing so benefit you?
You can simply set your account to private and then stop using it. That is the fastest way to handle this.
If you're new to the platform, as a very experienced UWer, I cannot recommend spending/wasting your time and money at this juncture.
Upwork has recently made a number of changes that have caused a complete collapse in the % of worthwhile clients (at least in my niche) while the number of FLs (both experienced and otherwise) competing for that tiny % remains overwhelming.
Perhaps things will get better in the near future but every response from UW management/support very clearly indicates that any optimism should be carefully measured, and then tossed into the trash where it belongs.
Best of luck to you.
Work smart, work safe!