TypeError: this.responsearray.find is not a function angular

I am getting the below error when trying to countryName in the response array.

TypeError: this.responsearray.find is not a function

Here is my ts code

this is what I declared

 responsearray: any;
      editCountry(row){
        let founditem = this.responsearray.find(item => item.countryName==row);
        console.log(founditem)
        if(founditem !== undefined){
        const dialogRef = this.dialog.open(popupcomponent, {
          width: '800px',
          panelClass: 'custom-modalbox',
          disableClose: true,
          data: {pageValue:founditem}   
        });

        dialogRef.afterClosed().subscribe(result => {
          console.log('The dialog was closed');
          if (!result) {
            this.loadData();
          }
        });
      }
      }

Here is my Interface

export interface assumption {
countryID: number;    
CountryName: string;
UserId: number;
UserName: string;
JoiningDate: String;
BirthDate: String;
OverallLength:number;}

Please let me know what I am doing wrong here.

responsearray should be Array and please Initialize it.