It is easy to use:
- select the DNA strand in plain text format (I preferably use this command for Primer3)
- activate Ubiquity (usually CTRL + Space)
- write the command revcomp
- you will see the reverse-complement counterpart of the DNA sequence you selected
- to copy it just press enter and it will be copied in your clipboard
To see the help, just write in Ubiquity: help revcomp
Install it: click here.