I'd say the first step is terima aja ke diri sendiri that you can't just "forget" that person. Memories of them will always pop up, and the feelings can still be there. It's okeeey. It's a part of the healing process. Then, when you feel like.. udah beneran gabisa forget them, you can focus on rebuilding your life. Focus on doing things that make you happy and spending time with people who make you happy. Kalau perlu, don't be afraid to reach out for extra support dari temen-temen kamu atau keluarga kamu.. if things still feel overwhelming.