Chris

You can do it yourself provided you do it to the legal standard, same as any DIY electrical work in your own home.

However, as you’re dealing with a very high amp ring and it may not have been used for a while, it is safer to get it checked by a qualified electrician. The high current drawn by an electric oven will generate heat at all the terminals where wires are joined, and the poorer the joins, the greater the risk that the heat could melt surrounding plastic or cause a fire.