Finish dungeon

I finish lvl200 mythic 3 how can i proceed to 201

Buy a Challenge map. it will take you to floor 201. after killing the cartographer it will drop a map for floor 202. and so on

Ok thanks

Easy option:
Set the floor to 200 --> go to Shop --> buy map --> finish map lvl 200 (there is always a cartographer at the end of all maps AND cartographers always gives map to next level) so 200–>201 and so on.

Slightly harder option:
Farm lvl 200 until you find a cartographer --> kill --> map for floor 201 --> farm

You can upgrade maps to whatever max level floor you have been at. So if you wanna farm floor 500 as fast as possible - set difficulty to the easiest level - rush maps from 200-500 on that easy level. When you reach floor 500 --> go back to floor 200 --> set difficulty to legend/mythic 3(whatever you like) --> buy map --> upgrade from 200-500 --> you will now have a floor lvl 500 map of whatever difficulty you choose --> go farm ^ ^

Also you could just do like I did, and farm all levels from 200-500 on as hard a difficulty as you can manage, trying to improve items along the way:)