access property of nested object based on dynamic string

Question

I have this object model:

export class FrcCapacity {
  constructor(
    public id?: number,
    public frcId?: number,
    public capGroupId?: number,
    public capGroup?: CapGroup,
    public salesProductId?: number,
    public p1?: number,
    public p2?: number,
    public p3?: number,
    public p4?: number,
    public p5?: number,
    public p6?: number,
    public p7?: number,
    public p8?: number,
    public p9?: number,
    public p10?: number,
    public p11?: number,
    public p12?: number,
    public total?: number
  ) {}
}

And I have an array of this, f. e. frcCapacity, filled with objects of the above object model.

I want to write a function, where I want to set the px value of the processed object. For this, I have all needed data and the function body looks like this:

periodValueChange(val: string, rowIndex: number, field: string) {
    for (let [key, value] of Object.entries(this.frcCapacity[rowIndex])) {
      if (key === field) this.frcCapacity[rowIndex]???
    }
  }

I'm trying this with Object.entries, but what should I write in place of the ???. How can I access the px field based on the field string parameter?

After some thinking and searching, this solution works:

periodValueChange(val: string, rowIndex: number, field: string) {
    let frcCap = this.frcCapacity[rowIndex];
    let map = new Map(Object.entries(frcCap));
    for (let [key, value] of map) {
      if (key === field) {
        map.set(field, +val);
      }
    }
    let obj = Array.from(map).reduce(
      (obj, [key, value]) => Object.assign(obj, { [key]: value }),
      {}
    );
    this.frcCapacity[rowIndex] = obj;
  }

Basically, I needed something like this:

periodValueChange(val: string, rowIndex: number, field: string) {
    this.frcCapacity[rowIndex].field = +val;
  }

Where the field parameter can be p1, p2, etc.