How can we Mark As Read only the processed email

Hi, I am reading the unread emails on FIFO basis order but I am processing only the Oldest Single email not all.

Like If I have 10 unread email like from 1 to 10 (Top to Bottom) So I am processing only the 10th email not all 1 to 9. But in outlook I am reading all unread email whole 10, And then bot makred all as reads email. But my requirement is to I want to mark only the Oldest single email which is 10th.
Rest from 1 to 9 mark are unread emails only. Please tell me how can I achieve this.
@Palaniyappan @ImPratham45 @Susana Kindly help