Typically you would just pull the curved spring bar out of the old strap and put into the new one. If you don't want to do that you can buy new ones. You need to specify the distance between the lugs.
One of my suppliers in the USA,
Esslinger sells a pack of 10 for $3. There must be suppliers closer to you.
An inexpensive (~$10-12 on Amazon) tool is used to gently bend the bars that need it. Without the tool, you can just do it with needle nose pliers and a jeweler's vise.