Hi @rizwanmgm
we can try an easy approach for this 🙂
see the demo list which i have created

see the demo flow designed for this
I am desiging a instant cloud flow for demo
step 1- use get items to get all items in the rating list

Step 2- Create an object which map the rating type with their values like below

Step 3- use apply to each action to loop through items present in list

inside the loop use update item action

For Ratings field in Update item > use below expression that maps the Rating type from object variable and gets the value and do calculation (multplication)

mul(variables('Values')?[items('Apply_to_each')?['Impact']],variables('Values')?[items('Apply_to_each')?['Risk']])
After running the flow> see below result in sharepoint list
Hope it helps !