Hi @khatriy,
You'll want to start by fixing the slope. This will involve some digging, so you'll need a garden fork to break up the soil, a shovel to pick it up and a wheelbarrow to take it away. Keep in mind that there will likely be drainage installed right behind the retaining wall, so you probably can't remove a load of material, but you can certainly remove the high spots and use them to fill up the low spots. During this process, try to remove as many stones as possible. A metal-tined rake will be handy for this.
With the groundwork complete, you can choose between re-turfing or reseeding the strip. Check out How To Lay Turf and How To Grow Grass From Lawn Seed for advice on either approach.
If you prefer to seed, loosen the soil surface to a fine texture, sow the appropriate lawn seed, and apply a light topdress of about 5–10mm of soil. Water daily until the new grass is well established, and avoid walking on the area during this time.
To support regrowth, apply a lawn starter fertiliser and consider a seaweed tonic to promote root health and reduce stress.
With this focused approach and the right materials, your lawn should recover smoothly and blend back into the existing turf line.
You might want to check out the Lawn section of our D.I.Y. advice pages for some further guidance.
Let me know if you have any further questions.
Jacob
