Combine text from multiple cells based on criteria from other cells

I have a large Bill of Quantities (more than 3000 rows).
The person who made it separated the description in column "C" into different rows which makes it impossible to sort by description which I need to do.
The only criteria that I can use is column "E".
For example I want to combine C4 to C6 into F6 and than delete rows 4 and 5 using weather E4 to E6 is empty or not.

Please help.

Try this approach
in F2 use the following formula and copy down

Formula:

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Now select data from A1 to F21 and apply filters. Apply a filter in column D to see all but (blanck).
If is this you want you can copy that and save in a new workbook.

See the file