This is a hard one to follow.
since we don't know your acronyms
I'll try to summarize:
you have (6) Columns:
A1) Date
B1) Product
C1) Op Stock
D1) In
E1) Out
F1) Closing Stock

It sounds like what you're wanting is to set the Op Stock (column C)
to the value of Closing Stock, and clear the values in In and Out.
I take it that Closing Stock is a formula that is (Op Stock) + IN - Out ??

If this is what you're asking, it's pretty simple.
If it is not, then you'll have to do a better job describing what you need.