Power Query Index help please

I am trying to create a portfolio tracking workbook, I have the following columns, Date, Time, Ticker, Action plus others.

Firstly its sorted by Date, Time, Ticker then Action.

The actions are B (Buy) & S (Sell)

The problem I have is one Buy action can have many Sell actions, eg: buy 2000, sell x 1000, Sell Sell 500, Sell 500 etc.

i am trying to number or index each Buy & sell action to something like this eg:

Buy#1 x 2000, Sell#1 1000, Sell#2 500, Sell#3 500 etc

any guidance would be appreciated greatly