Here we are going to assign posting period variant that we defined in our previous step. As I mentioned earlier we could assign one posting period variant to one or several company codes. From my experience it is better to go for one by one relation.
IMG Path: Financial Accounting (New) -> Financial Accounting Basic Settings (New) -> Ledgers -> Fiscal Year and Posting Periods -> Posting Periods -> Assign Variants to Company Code
After we open the transaction we should find our company code and fill the field for posting period variant. In my case Company code variant is named the same as the posting period variant which is preferred combination by most of the consultants.