The first step is to understand why the team cannot progress.
What is the challenge? Help them resolve it by removing obstacles, facilitating help/support/knowledge transfer from people or teams.
Encourage the team to complete it as unfinished items in sprints create a habit of leaving things behind.
Help the team to stay focused and finish the task.
On the other hand, if however the task is not resolvable,
make sure you discuss it in the retrospective
(1) understand why it turned out to be so?
For eg, Is this indicate the lack of skills which you need to address? Is it reflective of the lack of planning you have done? Is it the story itself? Is it inappropriate to include such unimportant tasks to sprints which takes up time but add no value?
(2) Agree to the action items/changes you would need to make so that this situation doesn't repeat.