How to show different levels/floors of indoor map ?

I have 2 different method of showing map but same question;

1. I have a local tile server which is running with docker. I've added different levels to my indoor map with josm indoorHelper plugin. How can i show/switch between these levels?
2. Different from this tile server, i am working on second map showing method. Have a flutter app and a plugin called mapsforge with it. I have the same indoor map. And plugins readme offers this code; new MapFileData( url: "https://raw.githubusercontent.com/mikes222/mapsforge_flutter/master/example/map_files/Chemnitz Uni.map", fileName: "Chemnitz Uni.map", displayedName: "Chemnitz - University (Indoor)", initialPositionLat: 50.81348, initialPositionLong: 12.92936, initialZoomLevel: 18, indoorZoomOverlay: true, indoorLevels: {1: 'OG', 0: 'EG', -1: 'UG'}, ), So there is a section indoorLevels: {1: 'OG', 0: 'EG', -1: 'UG'}, and when i write this code with my map, these levels shows nothing. How can i define my different levels?

To sum up with 1st and 2nd method i am having difficulties to show different levels/floors