It is a tricky one…
Try the below logic it worked for me
1)get the length of the string
2)repeat over the length
3)use substring to get the current character(by using beging index and end index increment them at the end of repeat)
4)convert the currentchar to upper case using toUpper
5)Branch on condition %currentchar% != %uppercasechar% and map the currentchar to string list and increnet string list indices.
- After all characters are repeated you will get all the small case characters into the string list.
Attached is screen shot of the flow service