I can’t quite tell completely based on the photo but those don’t look like LEDs one would “plug in”. It’s been a few years since I’ve dealt with LEDs that look roughly like the ones you got in that reel, but in my experience those need to be reflow soldered to metallic plugs with special pads for attaching wiring to them to power them. Trying to manually solder wiring to them to get them to work is not a simple process, can often cause them to short circuit, and not taking the appropriate care can ruin them.

Generally that type also burn so hot, that they need a custom metal slug as a heat sink to help cool them and redistribute the heat. Without the thermal help, they often melt/burn out almost immediately. Another issue that some don’t always realize or remember, depending on your electrical background, is that those types of LEDs have a polarity and need to be connected in the correct orientation or current won’t flow across them, thus making them appear not to work.

Of course, if you’ve done all this and they still don’t work…