Contact a general practitioner and undergo a health check at the border.
THE ACTUAL WORDING REMAINS THE SAME UNDER THE NEW MEASURE
According to point I/1 (only in Czech) the Ministry of the Czech Republic orders:
1. to all persons who have entered the territory of the Czech Republic since 21 June 2021 at 00:00,
a) in the event of any symptoms of an incipient infectious disease (in particular increased temperature, cough, shortness of breath, digestive difficulties, loss of smell, general weakness, or other symptoms), immediately report this fact by telephone or other remote access, to their registering general practitioner or pediatric and adolescent health care provider or, if they do not have a registering provider, to any general practitioner or pediatric and adolescent health care provider,
(b) to tolerate an inspection for signs of infectious disease when crossing the State border and, if signs of infectious disease are detected, to provide the necessary assistance to health professionals in the collection of a biological sample to detect the presence of SARS-CoV-2.
The full wording of the measure can be found here (only in Czech).