Hi!
"The unique identifier in both the forms will be the candidate's email ID"
You mean the unique identifier is the candidate's email address?
If so, you can use 'List rows present in a table' action block, filter its results to obtain the row with candidate's email address.
You can use either an ODATA expression as filter query input on 'List rows present in a table' or add a 'Filter array' action block assigning as its input 'List rows present in a table' output.
The tricky point is that both approaches will provide you an array with one element, so you need to read its values in order to update the row. The easiest way to do it is by means of an Apply to Each, as explained here
https://powerusers.microsoft.com/t5/Connecting-To-Data/Help-using-Flow-to-update-row-in-Excel/td-p/200530
BTW How many rows do you plan to have in your Excel table?
Thanx!