It sounds like you have a problem with one half of your LED Christmas light string not working. Based on your description, it's likely that there is a fault in the second half of the string or that the fuse in that half has blown.
Repairing this type of LED Christmas light string can be challenging, as the fuses are often built into the plugs at either end, and they may not be a standard size or type that can be easily replaced. However, it's worth checking the fuse to see if it is the issue before considering other options.
One way to access the fuse is to try to pry open the plug with a small screwdriver. However, this can be difficult to do without damaging the plug, so proceed with caution. Once you have accessed the fuse, you can check to see if it is blown and replace it if necessary. If the fuse appears to be fine and you are still experiencing the problem, then it may be a more serious issue with the circuit and it's probably best to discard the string.
Another option is to cut the string in two and insulate and seal the cut end with heat shrink tubing. This can be a good solution if you are unable to repair the string, but keep in mind that it may not be as aesthetically pleasing and you will have to discard half the string.
It's also important to keep in mind that most of the LED Christmas light string are not intended to be repairable, so troubleshooting and repair may not be easy or cost-effective. In this case, it's probably best to consider purchasing a new light string.