Auto-fill to last column of data and then to last row of data

Hello to everyone,

I would like to look for the last used cell in column 1, then grab L4 and auto-fill it up to the last used cell in column 1. Then auto-fill the range down to the last used row.

In the attachment, AQ1 is the last used cell, so I would like to auto-fill L4 to AQ4. Then grab L4:AQ4 and auto-fill it down to row 41.

Hopefully someone can help with the above as I've been struggling for a day editing other macros I've found online with no success.

Thank you