Late entry in Survival Analysis

I would like to ask how to deal with new entries of individuals in Survival Analysis. I have a study about the time to event of several individuals who suffer from a disease. The study starts on a specified date (let's assume 1/1/2019). The individuals on this date are 50. The study lasts 6 months. In these 6 months, more individuals must be included but they were not present on the starting date.

I have not any left censoring because, for the new individuals, the time they enter the study, is the time the symptoms appeared.

How should I deal with this late entry in the study?

I repeat the fact that, the date they enter, coincides with the manifestation of the disease. We can imagine the individuals as patients if that makes things easier.