There two ways, the easiest is to use the 'in' operator.
if ({PATIENT_LAB_RESULTS.FOREIGN_ANALYTE_DESCRIPTION} in ["KT/V DAUGIRDAS", "KT/V (DAUGIRDAS))", "KT/V - [DOQI-DG]"] then "KT/V DAUGIRDAS" else
{PATIENT_LAB_RESULTS.FOREIGN_ANALYTE_DESCRIPTION}
otherwise you will have to repeat the comparision three times seperated by 'OR's.
if ({PATIENT_LAB_RESULTS.FOREIGN_ANALYTE_DESCRIPTION} = "KT/V DAUGIRDAS" OR ({PATIENT_LAB_RESULTS.FOREIGN_ANALYTE_DESCRIPTION} ="KT/V (DAUGIRDAS))" OR ({PATIENT_LAB_RESULTS.FOREIGN_ANALYTE_DESCRIPTION} = "KT/V - [DOQI-DG]" then "KT/V DAUGIRDAS" else
{PATIENT_LAB_RESULTS.FOREIGN_ANALYTE_DESCRIPTION}