How to update a value in another form in CRM 2016 using Javascript?

Can someone tell me how I can update a value in another entity?

I'm currently on the Order Form (SalesOrder entity) and when I update the Order Date field, I want this to update a field on the Order Product form (SalesOrderDetail entity).

For privacy reasons, I cannot paste the actual code since it's part of my company's intellectual property. So I was hoping my examples would be enough for someone to help me.

I saw something like this to pull data from the SalesOrderDetail entity on the Order form - but cant seem to update it.

 var odataSelect = serverUrl + "/xrmservices/2011/OrganizationData.svc/SalesOrderDetailSet?$select=BaseAmount,BaseAmount_Base,Description,ExchangeRate,ExtendedAmount,ExtendedAmount_Base,IsPriceOverridden,IsProductOverridden,ManualDiscountAmount,ManualDiscountAmount_Base,neu_Modified,neu_PercentDiscount,PricePerUnit,PricePerUnit_Base,PricingErrorCode,ProductDescription,ProductId,Quantity,WillCall&$filter=QuantityBackordered gt 0 and SalesOrderId/Id eq guid'" + oldOrderId + "'";

Any guidance would greatly be appreciated! Thank you in advance!