Pull cord starter ropes are fairly simple to replace.
The most common width of lawnmower starter rope is 3.5 mm . I use this on all my lawnmowers and never have a problem.
You can buy the correct length rope with the handle attached here.Universal Lawnmower Starter Pull Handle & Cord Line/Rope Mower Engine Petrol
If you are planning on replacing lots of starter rope it is advisable to buy it in 30 metre lenghts and attach the handle yourself
You can find this here Oregon 522852 Heavy Duty Professional Starter Rope
You can buy individual handles here Mountfield Genuine 18550052/0 Starter Handle
Here’s a video teaching how to replace the starter recoil rope.
Leave me a comment on my Youtube channel if you can’t find a part. Just post your question on the comments section of any video and I will get back to you.
You can find my channel here https://www.youtube.com/c/MowerMan