Hi Sanjeev,

Thanks for posting on PSC.

Navigate to Record Explorer->Decision->Declare Expression(click on it). It will display all the declare expressions in the application. 

Select the desired declare expression rule to open, you can see the configuration of that particular declare expression and modify it as per your requirement.

To Answer your second questions:- "I don't understand what is OOTB but what I mean is that if I make a declare expression on a property and I want to revisit this expression then how do I do it? How can I know whether there is any associated declare expression with a property? "

OOTB mean Out of the Box. In pega, it's used for referring all the rules which are packaged with default Pega ruleset.  

If you want to revisit the declare expression which you might have created on a property earlier, kindly follow the below steps:-

1. Open the property rule.

2. Go to Advanced Tab.

3. Click "Explore" button located at down side.

4. Select "Expression" tab.

5. Here you go, all associated declare expressions are available.

Refer screenshot below, I have checked for OOTB "pyPageRef" property.

Kindly notify and mark as answered, if it helps.

Thanks,

Asif