According to few articles I read (like BBC about The people with hidden immunity against Covid-19 ):
starting out about four or five days after infection, you begin to see T cells getting activated, and indications they are specifically recognising cells infected with the virus,” says Hayday. These unlucky cells are then dispatched quickly and brutally – either directly by the T cells themselves, or by other parts of the immune system they recruit to do the unpleasant task for them – before the virus has a chance to turn them into factories that churn out more copies of itself.
When virus just entered a cell, but had no chance to churn more copies: Is surface of the cell any different? How T-cell can distinguish infected cell from non-infected?
I am no biologist, but I am fascinated about biology now, and curious to learn more. Sorry if I am not using proper terminology.
I found How do T-cells determine which cells they've already inspected? , but T-cell activation is mentioned only in the context of dendritic cells and lymph nodes. IIUC, T-cells should attack lungs cells to eliminate cells infected by covid-19 there.