How to succesfully edit 19,822 cells with a single value on an Excel spreadsheet for an unpaid assignment using open source software

The following is a (manual) log on my procedure for solving a "Basic Excel" assignment for a Tech Support freelance job on Upwork. I wonder if this is a common approach to software coming from technology professionals or if there's something I did wrong here. It was surprising how challenging this was to me. Even more after realizing how simple and short the "solution" I came up with was.

Job Title:
Technical Customer Support

Assignment:
The attached file named WalmartUS-Promo-All-Clearance-020923 is a walmart promotion feed. I would like you to change the start date to February 12th 2023 at time 9AM. The End date I would like changed to May 30th at time 1AM. Everything else left the same. Its important to note this spreadsheet has macros which can break easily if incorrectly saved. Walmart will not accept invalid spreadsheets, if you spreadsheet is correctly saved without issues, walmart will tell us with a validity check.

First attempt
OS: Windows 10
Software: LibreOffice Calc (not sure about the version)

1. I just assumed that the document had a reasonable length. Then I selected all rows from the "First date" column (by clicking the top column letter).
2. I unselected rows 1 - 4.
3. I pasted "12-02-2023 09:00:00"
4. My PC crashed or took longer to load than my patience could bear with.
5. Thought it was a Macros/format compatibility issue
6. Googled a bit about Macros-enabled files, crashes and LibreOffice, did not figure out if it was related.
7. Decided to try on a different PC.


Second attempt
OS: Kubuntu 20.04
Software: LibreOffice Calc 6.4.7.2

1. Repeated steps 1 to 6 from first attempt with the same result.
7. Then realized I was asking my PC to process over a million rows.
8. Read this article https://absentdata.com/excel/bypass-excel-row-limit-and-analyze-1m-rows/
9. Realized that LibreOffice Calc did not have PowerQuery Editor (which I am a bit familiar with)
10. Researched some alternatives. Tried to install LibreOffice Base.
11. sudo apt install libreoffice-base
12. "503 Service Unavailable" apt is broken on my PC for some reason. Unable to connect to any repository. Not even from the Software Center (an issue I had months ago and haven't bothered in fixing).
13. Googled "Excel Online" or "Power Query online" looking for a webapp. No workable results.
14. Decided to try Microsoft 365 even though I have no subscription.

Third attempt
OS: Kubuntu 20.04
Software: Microsoft 365 (www.office.com) on Firefox

1. No Power Query due to limited features from the free license.
2. Repeated steps 1 to 3 from 1st and 2nd attempts. Surprisingly, this time it worked.
5. Downloaded a copy.
6. Realized this copy was around 10MB larger than the original file.
7. Typed on the "Name box" field: "300000", then "200000", then "50000" and so on, until seeing some cells with content from the original files at row 9916.
8. Struggled to find a way to select cells I5:I9916 using the "name box" and then replacing them with the new date.
9. Switched to LibreOffice again.

Fourth attempt
OS: Kubuntu 20.04
Program: LibreOffice Calc 6.4.7.2

1. Struggled to find out a way to select rows I5:I9916 using the "name box" and then replacing them with the new date.
2. Googled "how to select rows without clicking and dragging" unsuccessfully.
3. Re-read the job description: "Basic Microsoft Excel skills". Started to lose my self-esteem.
4. Asked ChatGPT. Repeated the same question 3 or 4 times because it was forgetting stuff. Ended up frustrated.
5. Thinking about making excuses or ignoring the assignment hoping that they will still go further with my application.
6. Asked my relatives in desperation. They suggested something that didn't work and that I don't even remember.
7. "What if I just do it manually?" Just tried to manually click and drag from cells I5 to I9916. Range was successfully selected. Spent 30 seconds on it.
8. Ctrl + V "12-02-2023 09:00:00"
9. Then manually clicked and dragged from cells J9916 to J5. Again just 30 seconds.
10. Ctrl + V "30-05-2023 01:00:00"
11. Saved as .XLSM. Assignment completed.

12. Uploaded the resulting file to Upwork.

P.S. Somewhere between attempts two and four I also freaked out thinking I had been victim of a malicious macros file, scanned it on VirusTotal (all good) and re-visited the clients' profile who seemed legit.