Excel 2007 – converting existing numbers to numbers with decimals

Hello All first time on here.

I’m currently working with in a Microsoft Excel 2007 worksheet that has 570K+ rows.

One of the columns has numbers -0000027, -0000048, -0000102 etc

My problems is that I received this file in .txt format, converted it to .xlsx. The numbers displayed above are actually incorrect, they should be decimal places eg. -0000027 should be -0.27.

I have tried using the Excel Option, Advanced then clicking the box for 2 decimal places.

Problem is the only way to update the cells to reflect the change is when I individually click on the cell and then hit enter. Given I have 570K+ rows is there an easier way.

I would really appreciate any help you may be able to provide.