Explanation
Graphical user interface, text, application, email Description automatically generated

Here are the steps you must follow to add custom controls to a business process flow:
Step 1: Configure custom controls on a related entity.
Step 2: Generate and exporting the business process flow form.
Step 3: Copy custom control configurations to the FormXML for the business process flow.
Step 4: Import customizations into the Microsoft Dataverse environment.
Note:
Configure custom controls on a related table form.
Generate and exporting the business process flow form.
Copy custom control configurations to the business process flow form from the related table form.
Import the customizations back into Microsoft Dataverse.
Reference:
https://docs.microsoft.com/en-us/power-automate/custom-controls-business-process-flows