Business Requirement
Users want to see and update account record details associated to an opportunity on opportunity lightning record page.
Solution
You might be thinking of writing a custom Aura or Lightning Web Component to achieve this, but i believe in click not code..!!!
Lightning App Builder comes up with many inbuilt standard component to give you flexibility to build interactive application in Salesforce Lightning Experience.
Related Record Component is one of them which gives you the ability to show the action related to a record or its parent record of type create a record or update a record on the record page layout.
Steps to follow
In our case, we want to show account details on the opportunity record page, We will first create one action on account object of type update a record.
- From the object management settings for account, go to Buttons, Links, and Actions and click New Action.
- Verify that the action type is Update a Record.Actions can do more than just update records. To learn more about the other options, read the Action Categories and Types help article.
- Enter Edit Account in the Label field.

Click on save and it will open the layout to add the field you want on your action.

Once you have added the desired field on the action layout, click on save. Its time to add this action on contact record lightning page using lightning app builder.
- Open a Opportunity record page
- From Setup, select edit page option.
- Add the Related record Component on the canvas.
- In the properties pane, select Account Name as Lookup field
- Select the action you have just created in update action drop-down

Its time to save and activate the page if not already activated.
Results

As you can see, Account records are editable from Opportunity record page itself without writing a single line of code. Click not code…!!!
How should I do the other way? SHOWING EDITABLE Child RECORD DETAILS / Field(s) ON Parent RECORD LIGHTNING PAGE WITHOUT CODE IN SALESFORCE LIGHTNING EXPERIENCE
How to achieve this using LWC ?
You can make use of record-edit-form by passing the parent id and placing the component on the child record page. To know more, you can book a free 1:1 meeting with me at https://topmate.io/sanket_kumar