What kind of beads are they? Hobbycraft sell various kinds of thread wire or nylon. You will most likely need new fasterns as well. If you look on YouTube there are videos you could follow but it does depend on your beads as well. I've both made and mended lots of jewellery but it wouldn't be easy to describe to you what to do, a video is best. Elegran has given you a good answer too so you could go for that option. Good luck.
Recently two of my favourite necklaces have snapped and the beads scattered all over the floor. On both occasions I have saved the majority of the beads and want to restring them. Do any GN members make or repair costume jewellery ?
If the answer is yes do you get the string/wire for the beads online/craft shop or ironmongers ?
Can anyone suggest a basic book on repairing jewellery please?