Hi delinea
You can use this query
UPDATEyourprefix_contentSETmetakey= 'Mauricio Macri' WHEREmetakey= ''
This will update all empty tables in metakey with Mauricio Macri value
If you want to update tables already having a value then you can use
UPDATEyourprefix_contentSETmetakey= 'Mauricio Macri' WHEREmetakey= 'your value'
Take always a backup of your table before to update it
Regards