It looks like you have one column using the point as the decimal separator and another using the comma for the decimal separator. To converted to the second column, there is a built-in option in Find and Replace.
Step 1 – Highlight the column.
Step 2 – Select Data > Find and Replace ( or type Shift-Command-R ) to open the Find and Replace options.
Step 3 – Select the check box in the middle to convert the decimal and click Change.
This will also remove any points used for thousand separators.