From Intermediate to Business proficiency in Japanese while not living in Japan

**Goal**: Move back to Japan in 3/4 years and work there. I am a Product Manager in tech and would love to continue doing that.

**Question**: How do I reach business proficiency (which for me means 1) Passing the N1, 2) Being confident that I can work in Japanese without big problems)? Would love to hear success stories, material that you leveraged, and anything useful in your opinion. See below from my starting point.

**Context**: I lived two years in Japan (as a graduate student) a while back, I went there knowing zero Japanese and learned quite a bit – I could have normal conversations with native and was prepping for N2. Now it’s been 6 years that I left Japan, and I have been pretty inconsistent with the studies – but never stopped completely. I started taking Japanese classes again after a relocation and I am in an N2 class, and I feel this is a right difficulty for me. I sometimes don’t remember “easy” kanji and I feel I am not as fluent in speaking as I was 6 years ago, but I think it is a matter of catching up again and be consistent.

Edited with more details given qs received.