Patching up plaster where new plug sockets have been added

Good morning and hoping people could help/advise me.

I had extra plug sockets added to one of the rooms in my new house and top of the stairs. This has resulted in the plaster being all broken away.

Could people advise me on what they think is the best material and what trowel/other items I may need.

Have attached a photo so you get a better idea.









Any advice and tips would be greatly appreciated.

Thanks in advance