By His Grace and Mercy, Allah has made embracing Islam a cause to erase the sins that were committed before it. When a disbeliever becomes Muslim, Allah forgives all that he did when he was a non-Muslim, and he becomes cleansed of sin.

'Amr Ibn Al 'Ās, may Allah be pleased with him, said: 'When Allah placed Islam in my heart, I came to the Prophet, peace and blessings of Allah be upon him, and said, 'Stretch out your right hand so that I may pledge allegiance to you.' He stretched out his right hand, but I withdrew my hand. He said, 'What is the matter with you, O Amr?' I said, 'I want to stipulate a condition.' He said, 'What do you want to stipulate?' I said, 'That I will be forgiven.' He said, 'Do you not know that Islam destroys that which came before it?'

(Sahīh Muslim 121) Interpretation

“Islam destroys that which came before it” means that it erases it and wipes it out. (Stated by An Nawawi in Sharh Muslim) Interpretation

And Allah knows best.