Step 1: click on the 'Landmarks' button
Step 2: search a location, accept buiding name, road name, address, postal code ...
Step 3: there will have few markers on the map, try to find it out. Click on the suitable one, you will see a popup up with location name and ADD button.
Step 4: click on the ADD button to add this location. Make sure it disappeared and の maker showed.
Congratulation, you did it. Repeat these steps for more markers. Max 15 markers allowed.
Step 1: click on the の maker you want to delete. You will see the location name with a dustbin button.
Step 2: Click the dustbin button to delete this landmark. Once the の marker disappeared, landmark deleted successfully.