Well, you don't connect a Magic Band to a ticket.
You should have people set up in your My Disney Experience account.
You assign a Magic Band to a person.
You assign a ticket to a person.
As PP said, if that Magic Band has already been assigned to a person, it cannot be re-assigned to a new person.
On a computer, go to DisneyWorld.Com and log into your account
Hover over My Disney Experience
Click on My MagicBands and Cards
Scroll down until you find the name of the appropriate person
Next to that person's name, it will show the number of Magic Bands or cards assigned to that person
Click on that number
It will now list all of the Magic Bands and cards (tickets) assigned to that person
For each Magic Band, it will say either "active" or "inactive"
Underneath that will be the number which appears on the back of the Magic Band. You can look at the Magic Band you want to use, and see if it is on the list for this person; if it is not, you can go back and see if it is on the list for a different person.
Ticket cards also will be listed, so you can check them as well.