Welcome to our community, Jose
There is no facility that allows this. If you are using
RoboHelp HTML version 7, you could configure the Environment such
that you are able to see the Index and Glossary pods side by side.
Then copy from the Index and paste into the Glossary.
Keep in mind that even though the terms may already exist in
the Index, you won't save all that much time if you had some form
of an import feature available. This is because your Index
certainly won't have the definitions you will need. They will have
to be added later for each term.
Cheers... Rick