How is it possible to change a block that changes all drawings?

Hello,

I encounter a problem, that i mistakenly change one block in a drawing(which i dont remember now) but it effects all the drawings which are using the same block and changed all of them.

Is it possible to change it all back to original. I dont remember how i did it in first place.

Thanks in advance.

If it is an XREF any changes on the original will be reflected through all subsequent drawings. If it is a block each drawing has a unique block definition and changing 1 drawing will not affect any others.