Salesforce Update quantity of quote lines within a quote with Apex

For salesforce, I want to be able to update a quantity of quote lines in a amended quote.

The Setup

I am running the contract amender api to create a amended opportunity -> quote:

public with sharing class AmendedContract{
    
    public QuoteModel load(String contractId, String context) {
        String quoteJSON = SBQQ.ServiceRouter.load('SBQQ.ContractManipulationAPI.ContractAmender', contractId, context);
        //system.debug('contract ID: ' + contractId);
        //system.debug('Quote Json:  ' + quoteJSON);  
        return (QuoteModel) JSON.deserialize(quoteJSON, QuoteModel.class);
    }
}

public with sharing class AmendContext {
    public Boolean returnOnlyQuoteId;
}

public String createAmendment(String cID)
{
    system.debug('-----AMENDMENT CREATION STARTED-----');
    AmendContext con1 = new AmendContext();
    //system.debug('AMEND CONTEXT CON1: ' + con1);
    con1.returnOnlyQuoteId = false;
    
    String contextJson = JSON.serialize(con1);
    AmendedContract amender = new AmendedContract();
    QuoteModel quote = amender.load(cID, contextJson);
    //system.debug('ABUL-QUOTEMODEL:     ' + quote);
    SBQQ__Quote__c quoteRec = quote.record;
    String quoteId = (String) quoteRec.Id;
    system.debug('Amended quote ID:     ' + quoteId);
    return quoteId;
}

I was able to retrace the quote id of the amended quote (quoteId) but the issues is what I need to do next.

What I need

I need to be able to take the quoteId that was created from the amendment and update the quote line items to have a new quantity.

Is there a possibility to update the quote lines and change the quantity field?

You can use SOQL and DML

List<SBQQ__QuoteLine__c> qlList = new List<SBQQ__QuoteLine__c>();

// quoteId is the record id of SBQQ__Quote__c 

for(SBQQ__QuoteLine__c ql:[SELECT id,SBQQ__Quantity__c FROM SBQQ__QuoteLine__c WHERE SBQQ__Quote__c = : quoteId]){

    // Replace the below line with the logic in which qty needs to be updated
    ql.SBQQ__Quantity__c  = ql.SBQQ__Quantity__c + 1;
    qlList.add(ql);
}

UPDATE qlList;