Many tools in MacVector store a history of sequences, or search terms, that you have previously used. For example, the Find dialog and Primer Design tools. This is accessed using a drop down menu to the right of the box where you would normally type, or paste, your sequence. This is to allow easy access to previously used sequences. This is quite useful when you are searching with the same primer over many sequences in the same session (although consider using the Primer Database for more permanent access to the same primer sequences).
However, sometimes you may want to wipe these and start afresh. Especially if you’ve mistyped a primer sequence, and keep forgetting not to use it!
All you need to do is right click, or CTRL click on the dropdown menu and you’ll access a menu that allows you to remove an entry or clear the history entirely. In the primer tools don’t confuse this with the drop down menu to access the primer database.