Go to the "Accounting" Module.

Open the "Chart of Accounts" page. The chart of accounts will be displayed as a tree structure with nodes under which accounts are included.

Expand the node under which the customer account or supplier account is located by clicking on the "+" button next to it.

Select the specific customer account or supplier account you want to link.

Click on the related accounts button.

Click on the "+" button to add a related account.

Search for the account you want to link (either the customer account or supplier account) and select it from the search results.

Click "Save" to save the linkage between the customer account and supplier account.