Would anyone have advise on how to add running count to excel cells, which already have text in them, and without removing the said text.

Few screenshots will follow to clarify my issue.

I have received a ton of sheets which have a test case name as a text/string in the C column and they are missing a running count from the beginning of the cell (not sure if the "running count" is the correct term). In the first screenshot you can see how I need them to be, as well as in the couple first rows of the second screenshot (column C). So the original text could be for example "Purchase order" and I want it to be "1. Purchase order" and the next cell would be "2. Purchase order" etc.

=COUNTIF($C$2:C2;C2)&". "&C2

Then you can copy/paste as values and delete helper column