This is hard to do in Looker Studio, and generally we recommend working with the data at your database level. For example, you could use SQL like this to separate out the sprint values:
SELECT
TRIM(t.sprint_value) AS Sprint,
t1.“Number of return”
FROM
your_jira_table t1,
UNNEST(SPLIT(t1.sprint, ‘,’)) AS t(sprint_value)
This would basically take each row with multiple sprints and separate it into one row per sprint. Then you can use Looker Studio’s counts and sums to get the numbers you’re looking for.