You appear to have posted this in an number of forums. That's bad form, you should stick to one thread. The same amount of time put into a straightforward search would have seen your question answered already. The answer can be found in the S5 manual, myriad search results or on Youtube. Long press on the message balloon instead of the unopened message. Then select forward from the popup menu.
Google search: forward text message s5
Top search result.
Or even better, upgrade to a better third party SMS app.
If you still have problems, post a .PNG
screen shot and provide details of your firmware version, app version, what you have tried, et cetera.