The Ranked Flex queue is a separate queue from the old system that isn't based on the old system's rating in the slightest. Solo Queue, which will be coming sometime fairly soon, will be. For now, pretend it's preseason 2-3, when hard resets for everyone to 1200 ELO (silver 5) happened every year. The 0 ELO bronze player could literally get matched with the highest ELO player in the game when the reset happened. In the Ranked Flex, you are no longer whatever rank you had in Dynamic Queue beforehand - that will transfer to solo queue. You are now Silver 5, 1200 MMR, and when Riot puts solo queue on in a few days, you can go back to your normal games and they'll go back to their normal games - or you can try to climb Ranked Flex queue and let this all work itself out and try for some juicy flex-unique end of season rewards. Remember that Flex was designed for playing ranked with friends, like Dynamic Queue, but as Solo Queue is the system that's going to be taken more seriously, they will soft reset that (your MMR will be 1200+previous season's/2 and people you play with/against will be around where you ended last year) and, as this is a new system, couldn't transfer the old rankings over.