Pushing objects into dynamic keys

I have an empty array, a value and an object. Since I have many objects, I would like to categorize them. Somehow like this:

ARRAY 
  KEY
    OBJECT
    OBJECT
  KEY
    OBJECT

This is the array, which is empty by default:

public serviceTable: Services[] = [];

This is its interface:

export interface Services {
  details:
    {
      service: string,
      description: string
    }
}

This is the object that I get from result:

data: {
  details: [
    {
      service: this.formMain.get('service')?.value,
      description: this.formMain.get('description')?.value
    }
  ]
}

And last but not least, this is how I try to define the dynamic key of that array and its object.

dialogRef.afterClosed().subscribe(result => {
  if (result) {
   if (!Object.keys(this.serviceTable)[result.section]) {
     // No section found, lets create it ...
     this.serviceTable[this.randomNumber] = [result];
     console.log(this.serviceTable, 'ServiceTable')
   }
   else {
     this.serviceTable[this.randomNumber].push()
   }
}

The if-statement works good but there is something wrong with else-statement since I get this error:

TS2339: Property 'push' does not exist on type 'Services'.

I probably get this error because this.serviceTable[this.randomNumber] is not an array.

So if the key (this.randomNumber) does not exist in the array, it will be created. But if it already exists, I want to add the new object into the same key.

So my goal is to loop the array and call all objects that belong to a specific key, somehow like this:

for (let item of this.serviceTable[3]) { // Instead of a number, it could also be a string. For instance, this.serviceTable['myCategory']
  console.log(item.service); // This should list all 'services' that belong to the key '3'
}

How can I do this?

---

See an example of my code on StackBlitz OR see the full code on BitBucket.

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