copy columns to other work sheet for variable number of rows

[Watersource]

Hello fellow excel/vba users,

I have a sheet (basically a csv sheet that has been opened in tab Data, and converted to columns) that contains a variable number of rows in a fixed format.
This sheet contains a header and a number of entries. Per entry, the value of column 1 needs to be upgraded.
I want to convert the beneath steps in a macro, so the user only has to press a button and the sheet is filled automatically.
I have tried to copy all rows of the same entry in one go but did not succeed on this. Is my conclusion correct that I need to go through all lines one by one?
What would be the mechanism to determine the number of rows and how can I create a for ... next loop to through all the lines?
One last question, in the source tab I have separate columns for debet and credit amounts, how can I translate this to one column where debet is a positive amount and credit is a negative amount?

Thank you for your help on this.

 

[Watersource]

As example the source and target sheets, per payment there is one entry, then the entry number needs to be increased.
Also the columns need to be evaluated, e.g. the debet and credit column should be translated to one amount column where amount is positive when origin is debet and negative when credit.