Hi @Dharunya_Devi,
I would recommend first setting variables equal to combinations of choice sets that you are going to need (or just one choice set value if multiple selections are not allowed). This can be done by setting variable(s) to the variable type ISet and assigning them to these combinations.
After that, I would query entity records based upon choice sets combinations. Then run a for each loop and use the assign activity to assign the record choice set field to the desired combination. Then use the Update Multiple Entity Records and input the newly updated record list to the input argument and should update all the records in the query with the respective choice set values.
Please let me know if this helps!