Hello aferoz, welcome to the forum.

Are you familiar with find and replace? (From the home tab, find the icon that looks like binoculars under Editing).

I would first find and replace all periods with blanks.
Find: "."
Replace: ""

Then I would find and replace all commas with periods:
Find: ","
Replace: "."

You can then format the numbers any way you want. Having actual commas typed into numbers will not all you to use formulas as Excel will read the number as a mix of numbers and text.

Let me know if this helps!

Steve