Is this for the MMR boosting? I find this unethical but divine-immortal accounts make this as livelihood.

AFAIK, the boost manually happens.

If you want to increase your rank, you just have to practice on your current rank and keep on playing. I'm just an ancient 7 rank came from Legend 1 after the calibration for the last season. My technique is to adjust my rank which is pos 5 and it worked for me.