You are using both design time (Marker1, Marker2 etc.) and run time (the ones created using the CreateMarker Blok) Markers.
Design time Markers are very easy to use and 'delete' (actually you hide them or make them visible). Design Time Markers cannot be 'deleted.'
Run time Markers can be 'deleted' by traversing a List of the Markers (similar to the process Tim described). What needs to be done is complex.
It is difficult to determine what you are trying to do because your Blocks image is barely readable.
When working with a Trak, it is often preferable to create a path using a LineString similar to what is described in Store map.features in tinydb - #4 by SteveJG . This example may be what you are attempting. Or perhaps this one: https://groups.google.com/g/mitappinventortest/c/ivLItSb1lIU/m/YKGxke66BQAJ