Angular-Ag-Grid - Dynamically add columns

In 2 cases, I need to add some columns to Ag-grid. In other cases, I just need the base column.

So in the constructor, I declare the grid like this:

this.gridOption.columnDefs = [
  {
        headerName: 'Admission date',
        field: 'admissionPlannedDate',
        cellRendererFramework: DateCellRendererComponent,
        cellRendererParams: (params) => {
          return (params.data.admissionPlannedDate ? {dateFormat: 'dd.MM.yyyy - HH:mm'} : {dateFormat: ' '});
        },
        cellStyle: function (params) {
          return (params.data.admissionPlannedDate < new Date() ? {color: 'red'} : {});
        }
      },
      {
        headerName: 'Lastname',
        field: 'lastName',
        cellStyle: function (params) {
          return (params.data.edsId === null ? {color: 'orange'} : {});
        }
        },
      },
      {
        headerName: 'Sex',
        field: 'sex',
      },
      {
        headerName: 'Birthdate',
        field: 'birthDate',
        cellRendererFramework: DateCellRendererComponent,
        cellRendererParams: (params) => {
            return (params.data.birthDate ? {dateFormat: 'dd.MM.yyyy'} : {dateFormat: ' '});
        },
      },
      {
        headerName: 'Localisation',
        field: 'localisation',
      }
];

Then in my ngOnInit, in some cases, I need to add columns to my ag-grid.

I have tried the following:

 this.gridOption.columnDefs.push(
                {
                  headerName: 'Block',
                  field: 'block',
                }, {
                  headerName: 'SDS/Hosp',
                  field: 'sdsOrHosp'
                }
              );
console.log(this.gridOption); //I see the new columns here so the add worked but i don't see them visual in my grid

also tried

 this.gridOption.columnDefs.push({ headerName: 'Bloc', field:'block'});
 this.gridOption.columnDefs.push({ headerName: 'SDS/Hosp', field:'SDSorHosp'});

Does anyone have an idea? thanks