@Seunghui

Very helpful, thank you!  I needed this conjugation

이다-였(었)다

있다-있었다 

Now my question is,  how is 였어 different from  였(었)?  

 <font color="#000000">바보 </font>였어<font color="#000000">  and</font>  <font color="#000000">바보</font>였(었)

or

생일이었어요 and 생일이었었요

이다-였(었)다

있다-있었다 

어제 재미<font style="background-color: yellow;">있었</font>어요

 -Yesterday I had fun!

You can understand like this: fun was exist yesterday.

And "있다" has similar meaning with "can", so

참을수 <font style="background-color: yellow;">있었</font>다. 

means "I could restrain myself" 

내가<font color="#000000"> </font><font style="background-color: yellow;"><font color="#000000" style="background-color: rgb(255, 255, 255);">바보</font>였(었)</font>나봐 

--"바보" means stupid man or dull person,

you can understand like this: I 'was' a stupid person. 

I am not good at English (sob

But I hope my answer is helpful for you.. 

Sorrrrrry!

"있었" and "였었" mean something that was but isn't anymore. So,

통통한 아이였었어요. This would mean that you were a chubby kid, but have since lost the weight and are not anymore(the last part is understood from context).

Any verb that uses this particle has that meaning.

아빠가 서울에 갔었어요. Dad went to Seoul(and returned).