Hello Ann,
There is actually a very simple way to do this in OpaVote.
On the results page for your contest, click the "Recount Ballots" button. In the method selector choose the "Single Winner" checkbox method. Then click the "Recount Ballots" button.
OpaVote will recount the ballots as if it were a single-winner election with checkbox voting, using each voter's first choice. You can hover over the results graph to see how many votes each candidate has to then determine which candidate in the tie has the most votes.
You can experiment with that feature on our
demo election for Most Valuable Player. It is a Condorcet election, not Borda, but the process is the same.
You can also try it with a test election you create. All elections with up to 25 voters and 10 candidates are free.