<nz-form-item>
<nz-form-label nzRequired nzSpan="7"></nz-form-label>
<nz-form-control nzSpan="10">
<nz-select formControlName="roomId" nzAllowClear nzShowSearch (nzOnSearch)="onSearchRoom($event)" (ngModelChange)="onSearchCustomer()">
<nz-option *ngFor="let item of roomList" [nzValue]="item.room_id" [nzLabel]="item.room_no"></nz-option>
</nz-select>
<nz-form-explain *ngIf="isInvalid("roomId")"></nz-form-explain>
</nz-form-control>
</nz-form-item>
async onSearchRoom(search?) {
const { data } = await this.api.get("repair/rooms")({
room_no: search,
});
this.roomList = data;
console.log("change room")
}
async onSearchCustomer() {
const { data } = await this.api.get("repair/get-customer-by-room")({
room_id: this.add.value.roomId,
});
this.customer_id = data.customer_id
console.log(data.customer_name)
this.add.setValue({
customerName: data.customer_name,
roomId: this.add.value.roomId,
repairPerson: this.add.value.repairPerson,
repairPhone: this.add.value.repairPhone,
repairTime: this.add.value.repairTime,
repairOrderTime: this.add.value.repairOrderTime,
// projectId: this.add.value.projectId,
projectName: this.add.value.projectName,
repairCostType: this.add.value.repairCostType,
repairCostPrice: this.add.value.repairCostPrice,
})
} 
the choice you want to achieve is to apply for option changes in the repair room and request the associated household to assign a value to the household who applied for repair, but will always call onSearchCustomer.