Question: how to change date format yyyy-mm-dd to dd-mm-yyyy?
Answer: Step 1: Extract the year. =LEFT(A1,4) => 2018.
Step 2: Extract the day. =RIGHT(A1,2) => 25.
Step 3: Extract the month. This step is a little bit more difficult because you must extract 2 characters in the middle of your string. ... 
Step 4: Convert each part as a date.