Found Blink Mini

I am a maintenance man at a apartment complex and I found a blink mini and I thought I’d keep it but after downloading app discovered it registered. Can It be unregistered and used?

Nope.
To find out why, use the search icon here (magnify glass) and type in pre registered, already registered, etc. The search function is like Google.

No, they cannot be de-registered without Blink’s assistance, but they will do nothing unless you can prove it was a genuine purchase, from a reputable source, where the product should not have been registered when you made the purchase. Clearly, in your case, you are not going to be able to provide that, so it is now rendered useless.

They go on sale for 25 bucks from time to time at Amazon - USA. Watch for a deal if you really want one. Typical full price is 35. Be advised even though they are externally powered and don’t use batteries, they do NOT have continuous live view feed. Can’t use is for a baby monitor and things like that. Plenty of youtube videos out there reviewing Blink indoor mini to show what it can and can’t do as well as how well it performs.