What should I do after I lied to a young man, telling him that my friend he is speaking with tells his friends about him, even though I don't know him or his name, and then I repented from that?

The girl should be advised before informing her brother about her speaking to a foreign young man. When informing, one must be truthful and not exaggerate. The current obligation is to repent to Allah for lying by ceasing it, feeling remorse, and resolving not to return to it.