There is no reset. Resets are bad. They’ve been collecting role specific data to calculate your 3 role MMR values for a number of months. My guess is that if you’ve only played 1 role in comp for the last year, then they’ll just use that same MMR as a starting place for all 3 role placements, but maybe the ones they have less data on will be adjusted more significantly due to the lack of certainty on them.