Hello Soyoon,
As far as i know Indexing is not available in QuickSight yet .May be you can explore Rank or DenseRank function and check if that can be used in your case. if possible good to have that from the backend itself.
Nevertheless, you can refer this old post to get some idea -How to add a new column in (Row ID) which is sequentially increasing - #2 by robdhondt
Hope this helps.
Cheers,
Deep