How to retrieve values from table in description (system field)

[Shahrul Saifuddin]

||Month'Year||Spends(k USD)||
|Aug'21|210.1|
|Sep'21|120.6|
|Oct'21|250.1|
|Nov'21|321.8|
|Dec'21|128.5|
|Jan'22|321.3|
|Feb'22|201.6|
|Mar'22|215.3|
|Apr'22|222.0|
|May'22|158.6|
|Jun'22|312.5|
|July'22|265.2|
|Aug'22|128.3|

Hi Guys!

I want to know how can I add the last 5 values from the Spends column and then auto-populate it into another custom field.