Updating 20k+ rows from Excel to access. vbscript? VBA? SQL?

Any suggestions?

Some of these rows only need a few columns updated, and others need
all of them updated. If possible if say row 800 column 'S' is filled
in the access DB but is blank on the excel spread***, if possible i
like to keep the existing data in access and over right it with a
blank cell.

The spread*** is a export of the access DB, changes were made/merged
from other spreadsheets so the Unique ID is the same and in column A.

A script suggestions to complete this?

Thanks :)

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