Hey Serkan,
You need to modify the models/forms/marker.xml (either in administrator/components/com_hotspots or in components/com_hotspots - depending if you want the changes in the frontend or backend).
find the following field
<field name="hotspotText" type="editor" class="inputbox required"
label="COM_HOTSPOTS_FIELD_DESCRIPTION" description="COM_HOTSPOTS_FIELD_DESCRIPTION_DESC"
filter="JComponentHelper::filterText" buttons="article,image,pagebreak" required="true"/>
change it to:
<field name="hotspotText" type="editor" class="inputbox required"
default="test<br />test"
label="COM_HOTSPOTS_FIELD_DESCRIPTION" description="COM_HOTSPOTS_FIELD_DESCRIPTION_DESC"
filter="JComponentHelper::filterText" buttons="article,image,pagebreak" required="true"/>
to use <br /> to create a new line you need to encode it as in the example.
Kind regards,
Daniel