05 Thefirstcharacter PIC X.
05 FILLER PIC X.
05 Thelastcharacter PIC X.
Put your three-digit number to be reversed into Thenumber.
Then your preferred conditional construct which says:
If Thefirstcharacter equals "1", put Thelastcharacter into Thefirstcharacter and put "1" into Thelastcharacter, otherwise if Thefirstcharacter equals "2", put Thelastcharacter into Thefirstcharacter and put "2" into Thelastcharacter, otherwise, etc
In the real world, should also validate that the original "number" is actually a number.
Can't think why you'd want to do this, except for homework. I think all the "big guys" on here are very patient, although having to make the same points repeatedly. Don't just ask for your homework to be done for you, have a go at it and if you get struck, show what you've done and explain the problem you have. Show what should happen to the data, and what does happen with your code.