Help dax while adding column

Hi yamina ,

Please try following Dax formulars.

Min date = 
VAR CurrentIndex = 'Table'[Index]
VAR PreviousDossier = MAXX(FILTER('Table', 'Table'[Index] = CurrentIndex -1), 'Table'[N_dossier_NUDOS])
VAR CurrentDossier = 'Table'[N_dossier_NUDOS]
RETURN
IF(
    PreviousDossier = CurrentDossier && CurrentDossier <> BLANK(),
    MINX(FILTER('Table', 'Table'[N_dossier_NUDOS] = CurrentDossier), 'Table'[Date_creation_DACRI]),
    BLANK()
)

Condition retour = 
VAR CurrentDossier = 'Table'[N_dossier_NUDOS]
VAR CurrentIndex = 'Table'[Index]
VAR FirstDossierIndex = MINX(FILTER('Table', 'Table'[N_dossier_NUDOS] = CurrentDossier),'Table'[Index])
VAR FirstDossierCreationDate = CALCULATE(SELECTEDVALUE('Table'[Date_creation_DACRI]), 'Table'[Index] = FirstDossierIndex , ALL())
VAR CurrentPresentation = 'Table'[N_prestation_RGOUV]
VAR PreviousPresentation =  MAXX(FILTER('Table', 'Table'[Index] = CurrentIndex -1), 'Table'[N_prestation_RGOUV])
RETURN

IFERROR(
    IF( 'Table'[Date_creation_DACRI] - FirstDossierCreationDate >= 0 && 'Table'[Date_creation_DACRI] - FirstDossierCreationDate <= 30 && CurrentPresentation >= PreviousPresentation +1,
        "Retour dans les 30 jours",
        BLANK()
    ),
    BLANK()
)

The final result is as follows. Hopefully it will meet your needs.

Please see the attached pbix for reference.

Best Regards,
Dengliang Li

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