That needs relaying by someone competent who can achieve an invisible repair. It's quite hard to judge how much the sharp sand will compress to get the blocks at the same level - might be better to bed on some semi-dry sharp sand and cement, especially as I presume you don't have a whacker. To stop it happening again it needs restraining with a suitable edging.
Was going to cement in the edging first . (Going off first piece of advice on this thread). Then place the blocks on sharp sand and hit in with a mallet to get to correct level