So you fitted a new switch. Didn't you check the old one first?
It looks like your cooker is gas but still needs an electrical supply for igniter, cooling fan, oven light etc. So, is the electrical supply OK? Is it OK right to the cooker?
If the fuse has gone, you'll obviously need to find out why.
If the electricsl supply is OK, you'll need to check the ignition transformer is getting power when you press the ignition button.
If there's 240V on the input to the ignition module when you press the button, it's probably a failed module.
Espares or Partsmaster etc are usually pretty good.
You might even find a YouTube video showing how to change the ignition transformer/module. Searching intelligently is key.