typescript property doesn't exist on type

I'm a newbie to the typescript, here I'm trying to update the mongo data based on pre-fetched data, in the console I'm getting all the data, but when I try to get the single key value getting an error of Property 'overallTotalMarks' does not exist on type

here below is a code what i tried

 const preExams = await this.examHistoryModel.find({userId:examHistoryData.userId});
    console.log(preExams) //this printing all the data in preExams
    if(preExams.length <= 0){
        const newHistory = new this.examHistoryModel(examHistoryData)
        const result = await newHistory.save()
        return result
    }
    else{            
        console.log(preExams.overallTotalMarks) //getting error on this line
        return "You have attempted the test already!";
    }

here is the mongo schema

export type ExamHistoryDocument = ExamHistory & Document;

 @Schema()

export class ExamHistory{
@Prop({required: true})
userId?: number;

@Prop({required: true})
overAllTime: Number;

@Prop({required: true, default:0})
overallTotalMarks: Number;

@Prop({required: true, default:0})
overallGainedMarks: Number;

@Prop({required: true, default:0})
overallCorrectAns: Number;

@Prop({required: true, default:0})
overallWrongAns: Number;

@Prop({required: true, default:0})
overallLeftQue: Number;


@Prop({required: true, default:'Fail'})
overallStatus: String;

@Prop({type:[SectionHistorySchema]})
sectionHistory: SectionHistory[];
}

 export const examHistorySchema = SchemaFactory.createForClass(ExamHistory)

any help or suggestions are really appriciated