If the tape is OK but the wraps have separated, you could try rewrapping. But most people would opt to replace the tape. The main trick to a good tape wrap is to stretch it as you go so it follows the handlebar curves smoothly. Depending on the tape, you may be able to stuff some inside the bar end and then attach the plug, or you may have to cut it flush with the bar end. If the tape comes with 2 short pieces, they go around the back of the brake levers before you start wrapping.