To select a repeat activate the Select tool:

<center>
     <br>
     <img src="/wiki/download/attachments/4227424/Selecting Repeat.png"/>
     <br>
</center>

and click on the repeat:

<center>
     <br>
     <img src="/wiki/download/attachments/4227424/Selecting Repeat_1.png"/>
     <br>
</center>

To deselect the repeat either click on other repeat or hold Ctrl and click somewhere on the dotplot.