For official documentation, which of the two constructions is correct English.

Relevant data are entered in the software.

or 

Relevant data is entered in the software.

I personally thing it should be "data is entered", but co-workers insist that since its more than one piece of data it should be plural. 

Any assistance would be greatly appreciated.

My Canadian Oxford Paperback Dictionary says this.

In scientific writing, data is almost always treated as a plural, but the singular use is standard in all other levels of writing.

In my experience this is true, although I know that people who object to this often have strong feelings on the matter. I worked in the computer business for many years, and we always said 'is'.

In your examples, I'm more concerned about the phrase '. . . data is entered in the software'.

Instead of this, I've always said and read things like

'data is entered using the XYZ software'

'XYZ is used to enter the data'

''Use XYZ to enter the data'

Best wishes, Clive