Every reset is different form what I heard. The time before this last one was called "the soft reset" in which they lowered everyone's MMR slightly from what it had been, then it had you re-qualify, and it put you in whatever league your MMR number fell in range of.
Your MMR is a magical number that has mostly to do with your win/loss. Of course, it's not just strictly based on your ratio. Games that you were expected to win are worth less MMR when you win, than games that you were expected to lose (based on adding the team's total MMR).
The reverse can be said if you lose. If you were supposed to lose, then you don't lose as much MMR, and if you were supposed to win, but you lost, you lose more MMR than you would if it were equal.
So for an example:
Your team average: 1000 MMR
Enemy team average: 1050 MMR
If your team wins, it will be an upset. Like the underdogs pulling through, and it will earn you more points than if you both had 1000. There is no actual way to see your MMR anymore, it was removed years ago. But it is still there. There are some websites that attempt to calculate your account's MMR, though they don't guarantee accuracy. I think I saw a little feature like this on OP.GG one time.